Struct clap::ArgMatches

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pub struct ArgMatches<'a> { /* private fields */ }
Expand description

Used to get information about the arguments that were supplied to the program at runtime by the user. New instances of this struct are obtained by using the App::get_matches family of methods.

§Examples

let matches = App::new("MyApp")
    .arg(Arg::with_name("out")
        .long("output")
        .required(true)
        .takes_value(true))
    .arg(Arg::with_name("debug")
        .short("d")
        .multiple(true))
    .arg(Arg::with_name("cfg")
        .short("c")
        .takes_value(true))
    .get_matches(); // builds the instance of ArgMatches

// to get information about the "cfg" argument we created, such as the value supplied we use
// various ArgMatches methods, such as ArgMatches::value_of
if let Some(c) = matches.value_of("cfg") {
    println!("Value for -c: {}", c);
}

// The ArgMatches::value_of method returns an Option because the user may not have supplied
// that argument at runtime. But if we specified that the argument was "required" as we did
// with the "out" argument, we can safely unwrap because `clap` verifies that was actually
// used at runtime.
println!("Value for --output: {}", matches.value_of("out").unwrap());

// You can check the presence of an argument
if matches.is_present("out") {
    // Another way to check if an argument was present, or if it occurred multiple times is to
    // use occurrences_of() which returns 0 if an argument isn't found at runtime, or the
    // number of times that it occurred, if it was. To allow an argument to appear more than
    // once, you must use the .multiple(true) method, otherwise it will only return 1 or 0.
    if matches.occurrences_of("debug") > 2 {
        println!("Debug mode is REALLY on, don't be crazy");
    } else {
        println!("Debug mode kind of on");
    }
}

Implementations§

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impl<'a> ArgMatches<'a>

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pub fn value_of<S: AsRef<str>>(&self, name: S) -> Option<&str>

Gets the value of a specific option or positional argument (i.e. an argument that takes an additional value at runtime). If the option wasn’t present at runtime it returns None.

NOTE: If getting a value for an option or positional argument that allows multiples, prefer ArgMatches::values_of as ArgMatches::value_of will only return the first value.

§Panics

This method will panic! if the value contains invalid UTF-8 code points.

§Examples
let m = App::new("myapp")
    .arg(Arg::with_name("output")
        .takes_value(true))
    .get_matches_from(vec!["myapp", "something"]);

assert_eq!(m.value_of("output"), Some("something"));
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pub fn value_of_lossy<S: AsRef<str>>(&'a self, name: S) -> Option<Cow<'a, str>>

Gets the lossy value of a specific argument. If the argument wasn’t present at runtime it returns None. A lossy value is one which contains invalid UTF-8 code points, those invalid points will be replaced with \u{FFFD}

NOTE: If getting a value for an option or positional argument that allows multiples, prefer Arg::values_of_lossy as value_of_lossy() will only return the first value.

§Examples
use std::ffi::OsString;
use std::os::unix::ffi::{OsStrExt,OsStringExt};

let m = App::new("utf8")
   .arg(Arg::from_usage("<arg> 'some arg'"))
   .get_matches_from(vec![OsString::from("myprog"),
                           // "Hi {0xe9}!"
                           OsString::from_vec(vec![b'H', b'i', b' ', 0xe9, b'!'])]);
assert_eq!(&*m.value_of_lossy("arg").unwrap(), "Hi \u{FFFD}!");
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pub fn value_of_os<S: AsRef<str>>(&self, name: S) -> Option<&OsStr>

Gets the OS version of a string value of a specific argument. If the option wasn’t present at runtime it returns None. An OS value on Unix-like systems is any series of bytes, regardless of whether or not they contain valid UTF-8 code points. Since Strings in Rust are guaranteed to be valid UTF-8, a valid filename on a Unix system as an argument value may contain invalid UTF-8 code points.

NOTE: If getting a value for an option or positional argument that allows multiples, prefer ArgMatches::values_of_os as Arg::value_of_os will only return the first value.

§Examples
use std::ffi::OsString;
use std::os::unix::ffi::{OsStrExt,OsStringExt};

let m = App::new("utf8")
   .arg(Arg::from_usage("<arg> 'some arg'"))
   .get_matches_from(vec![OsString::from("myprog"),
                           // "Hi {0xe9}!"
                           OsString::from_vec(vec![b'H', b'i', b' ', 0xe9, b'!'])]);
assert_eq!(&*m.value_of_os("arg").unwrap().as_bytes(), [b'H', b'i', b' ', 0xe9, b'!']);
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pub fn values_of<S: AsRef<str>>(&'a self, name: S) -> Option<Values<'a>>

Gets a Values struct which implements Iterator for values of a specific argument (i.e. an argument that takes multiple values at runtime). If the option wasn’t present at runtime it returns None

§Panics

This method will panic if any of the values contain invalid UTF-8 code points.

§Examples
let m = App::new("myprog")
    .arg(Arg::with_name("output")
        .multiple(true)
        .short("o")
        .takes_value(true))
    .get_matches_from(vec![
        "myprog", "-o", "val1", "val2", "val3"
    ]);
let vals: Vec<&str> = m.values_of("output").unwrap().collect();
assert_eq!(vals, ["val1", "val2", "val3"]);
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pub fn values_of_lossy<S: AsRef<str>>(&'a self, name: S) -> Option<Vec<String>>

Gets the lossy values of a specific argument. If the option wasn’t present at runtime it returns None. A lossy value is one where if it contains invalid UTF-8 code points, those invalid points will be replaced with \u{FFFD}

§Examples
use std::ffi::OsString;
use std::os::unix::ffi::OsStringExt;

let m = App::new("utf8")
   .arg(Arg::from_usage("<arg>... 'some arg'"))
   .get_matches_from(vec![OsString::from("myprog"),
                           // "Hi"
                           OsString::from_vec(vec![b'H', b'i']),
                           // "{0xe9}!"
                           OsString::from_vec(vec![0xe9, b'!'])]);
let mut itr = m.values_of_lossy("arg").unwrap().into_iter();
assert_eq!(&itr.next().unwrap()[..], "Hi");
assert_eq!(&itr.next().unwrap()[..], "\u{FFFD}!");
assert_eq!(itr.next(), None);
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pub fn values_of_os<S: AsRef<str>>(&'a self, name: S) -> Option<OsValues<'a>>

Gets a OsValues struct which is implements Iterator for OsString values of a specific argument. If the option wasn’t present at runtime it returns None. An OS value on Unix-like systems is any series of bytes, regardless of whether or not they contain valid UTF-8 code points. Since Strings in Rust are guaranteed to be valid UTF-8, a valid filename as an argument value on Linux (for example) may contain invalid UTF-8 code points.

§Examples
use std::ffi::{OsStr,OsString};
use std::os::unix::ffi::{OsStrExt,OsStringExt};

let m = App::new("utf8")
   .arg(Arg::from_usage("<arg>... 'some arg'"))
   .get_matches_from(vec![OsString::from("myprog"),
                               // "Hi"
                               OsString::from_vec(vec![b'H', b'i']),
                               // "{0xe9}!"
                               OsString::from_vec(vec![0xe9, b'!'])]);

let mut itr = m.values_of_os("arg").unwrap().into_iter();
assert_eq!(itr.next(), Some(OsStr::new("Hi")));
assert_eq!(itr.next(), Some(OsStr::from_bytes(&[0xe9, b'!'])));
assert_eq!(itr.next(), None);
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pub fn is_present<S: AsRef<str>>(&self, name: S) -> bool

Returns true if an argument was present at runtime, otherwise false.

§Examples
let m = App::new("myprog")
    .arg(Arg::with_name("debug")
        .short("d"))
    .get_matches_from(vec![
        "myprog", "-d"
    ]);

assert!(m.is_present("debug"));
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pub fn occurrences_of<S: AsRef<str>>(&self, name: S) -> u64

Returns the number of times an argument was used at runtime. If an argument isn’t present it will return 0.

NOTE: This returns the number of times the argument was used, not the number of values. For example, -o val1 val2 val3 -o val4 would return 2 (2 occurrences, but 4 values).

§Examples
let m = App::new("myprog")
    .arg(Arg::with_name("debug")
        .short("d")
        .multiple(true))
    .get_matches_from(vec![
        "myprog", "-d", "-d", "-d"
    ]);

assert_eq!(m.occurrences_of("debug"), 3);

This next example shows that counts actual uses of the argument, not just -’s

let m = App::new("myprog")
    .arg(Arg::with_name("debug")
        .short("d")
        .multiple(true))
    .arg(Arg::with_name("flag")
        .short("f"))
    .get_matches_from(vec![
        "myprog", "-ddfd"
    ]);

assert_eq!(m.occurrences_of("debug"), 3);
assert_eq!(m.occurrences_of("flag"), 1);
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pub fn index_of<S: AsRef<str>>(&self, name: S) -> Option<usize>

Gets the starting index of the argument in respect to all other arguments. Indices are similar to argv indices, but are not exactly 1:1.

For flags (i.e. those arguments which don’t have an associated value), indices refer to occurrence of the switch, such as -f, or --flag. However, for options the indices refer to the values -o val would therefore not represent two distinct indices, only the index for val would be recorded. This is by design.

Besides the flag/option descrepancy, the primary difference between an argv index and clap index, is that clap continues counting once all arguments have properly seperated, whereas an argv index does not.

The examples should clear this up.

NOTE: If an argument is allowed multiple times, this method will only give the first index.

§Examples

The argv indices are listed in the comments below. See how they correspond to the clap indices. Note that if it’s not listed in a clap index, this is becuase it’s not saved in in an ArgMatches struct for querying.

let m = App::new("myapp")
    .arg(Arg::with_name("flag")
        .short("f"))
    .arg(Arg::with_name("option")
        .short("o")
        .takes_value(true))
    .get_matches_from(vec!["myapp", "-f", "-o", "val"]);
            // ARGV idices: ^0       ^1    ^2    ^3
            // clap idices:          ^1          ^3

assert_eq!(m.index_of("flag"), Some(1));
assert_eq!(m.index_of("option"), Some(3));

Now notice, if we use one of the other styles of options:

let m = App::new("myapp")
    .arg(Arg::with_name("flag")
        .short("f"))
    .arg(Arg::with_name("option")
        .short("o")
        .takes_value(true))
    .get_matches_from(vec!["myapp", "-f", "-o=val"]);
            // ARGV idices: ^0       ^1    ^2
            // clap idices:          ^1       ^3

assert_eq!(m.index_of("flag"), Some(1));
assert_eq!(m.index_of("option"), Some(3));

Things become much more complicated, or clear if we look at a more complex combination of flags. Let’s also throw in the final option style for good measure.

let m = App::new("myapp")
    .arg(Arg::with_name("flag")
        .short("f"))
    .arg(Arg::with_name("flag2")
        .short("F"))
    .arg(Arg::with_name("flag3")
        .short("z"))
    .arg(Arg::with_name("option")
        .short("o")
        .takes_value(true))
    .get_matches_from(vec!["myapp", "-fzF", "-oval"]);
            // ARGV idices: ^0      ^1       ^2
            // clap idices:         ^1,2,3    ^5
            //
            // clap sees the above as 'myapp -f -z -F -o val'
            //                         ^0    ^1 ^2 ^3 ^4 ^5
assert_eq!(m.index_of("flag"), Some(1));
assert_eq!(m.index_of("flag2"), Some(3));
assert_eq!(m.index_of("flag3"), Some(2));
assert_eq!(m.index_of("option"), Some(5));

One final combination of flags/options to see how they combine:

let m = App::new("myapp")
    .arg(Arg::with_name("flag")
        .short("f"))
    .arg(Arg::with_name("flag2")
        .short("F"))
    .arg(Arg::with_name("flag3")
        .short("z"))
    .arg(Arg::with_name("option")
        .short("o")
        .takes_value(true)
        .multiple(true))
    .get_matches_from(vec!["myapp", "-fzFoval"]);
            // ARGV idices: ^0       ^1
            // clap idices:          ^1,2,3^5
            //
            // clap sees the above as 'myapp -f -z -F -o val'
            //                         ^0    ^1 ^2 ^3 ^4 ^5
assert_eq!(m.index_of("flag"), Some(1));
assert_eq!(m.index_of("flag2"), Some(3));
assert_eq!(m.index_of("flag3"), Some(2));
assert_eq!(m.index_of("option"), Some(5));

The last part to mention is when values are sent in multiple groups with a delimiter.

let m = App::new("myapp")
    .arg(Arg::with_name("option")
        .short("o")
        .takes_value(true)
        .multiple(true))
    .get_matches_from(vec!["myapp", "-o=val1,val2,val3"]);
            // ARGV idices: ^0       ^1
            // clap idices:             ^2   ^3   ^4
            //
            // clap sees the above as 'myapp -o val1 val2 val3'
            //                         ^0    ^1 ^2   ^3   ^4
assert_eq!(m.index_of("option"), Some(2));
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pub fn indices_of<S: AsRef<str>>(&'a self, name: S) -> Option<Indices<'a>>

Gets all indices of the argument in respect to all other arguments. Indices are similar to argv indices, but are not exactly 1:1.

For flags (i.e. those arguments which don’t have an associated value), indices refer to occurrence of the switch, such as -f, or --flag. However, for options the indices refer to the values -o val would therefore not represent two distinct indices, only the index for val would be recorded. This is by design.

NOTE: For more information about how clap indices compare to argv indices, see ArgMatches::index_of

§Examples
let m = App::new("myapp")
    .arg(Arg::with_name("option")
        .short("o")
        .takes_value(true)
        .use_delimiter(true)
        .multiple(true))
    .get_matches_from(vec!["myapp", "-o=val1,val2,val3"]);
            // ARGV idices: ^0       ^1
            // clap idices:             ^2   ^3   ^4
            //
            // clap sees the above as 'myapp -o val1 val2 val3'
            //                         ^0    ^1 ^2   ^3   ^4
assert_eq!(m.indices_of("option").unwrap().collect::<Vec<_>>(), &[2, 3, 4]);

Another quick example is when flags and options are used together

let m = App::new("myapp")
    .arg(Arg::with_name("option")
        .short("o")
        .takes_value(true)
        .multiple(true))
    .arg(Arg::with_name("flag")
        .short("f")
        .multiple(true))
    .get_matches_from(vec!["myapp", "-o", "val1", "-f", "-o", "val2", "-f"]);
            // ARGV idices: ^0       ^1    ^2      ^3    ^4    ^5      ^6
            // clap idices:                ^2      ^3          ^5      ^6

assert_eq!(m.indices_of("option").unwrap().collect::<Vec<_>>(), &[2, 5]);
assert_eq!(m.indices_of("flag").unwrap().collect::<Vec<_>>(), &[3, 6]);

One final example, which is an odd case; if we don’t use value delimiter as we did with the first example above instead of val1, val2 and val3 all being distinc values, they would all be a single value of val1,val2,val3, in which case case they’d only receive a single index.

let m = App::new("myapp")
    .arg(Arg::with_name("option")
        .short("o")
        .takes_value(true)
        .multiple(true))
    .get_matches_from(vec!["myapp", "-o=val1,val2,val3"]);
            // ARGV idices: ^0       ^1
            // clap idices:             ^2
            //
            // clap sees the above as 'myapp -o "val1,val2,val3"'
            //                         ^0    ^1  ^2
assert_eq!(m.indices_of("option").unwrap().collect::<Vec<_>>(), &[2]);
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pub fn subcommand_matches<S: AsRef<str>>( &self, name: S ) -> Option<&ArgMatches<'a>>

Because Subcommands are essentially “sub-Apps” they have their own ArgMatches as well. This method returns the ArgMatches for a particular subcommand or None if the subcommand wasn’t present at runtime.

§Examples
let app_m = App::new("myprog")
    .arg(Arg::with_name("debug")
        .short("d"))
    .subcommand(SubCommand::with_name("test")
        .arg(Arg::with_name("opt")
            .long("option")
            .takes_value(true)))
    .get_matches_from(vec![
        "myprog", "-d", "test", "--option", "val"
    ]);

// Both parent commands, and child subcommands can have arguments present at the same times
assert!(app_m.is_present("debug"));

// Get the subcommand's ArgMatches instance
if let Some(sub_m) = app_m.subcommand_matches("test") {
    // Use the struct like normal
    assert_eq!(sub_m.value_of("opt"), Some("val"));
}
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pub fn subcommand_name(&self) -> Option<&str>

Because Subcommands are essentially “sub-Apps” they have their own ArgMatches as well.But simply getting the sub-ArgMatches doesn’t help much if we don’t also know which subcommand was actually used. This method returns the name of the subcommand that was used at runtime, or None if one wasn’t.

NOTE: Subcommands form a hierarchy, where multiple subcommands can be used at runtime, but only a single subcommand from any group of sibling commands may used at once.

An ASCII art depiction may help explain this better…Using a fictional version of git as the demo subject. Imagine the following are all subcommands of git (note, the author is aware these aren’t actually all subcommands in the real git interface, but it makes explanation easier)

             Top Level App (git)                         TOP
                             |
      -----------------------------------------
     /             |                \          \
  clone          push              add       commit      LEVEL 1
    |           /    \            /    \       |
   url      origin   remote    ref    name   message     LEVEL 2
            /                  /\
         path            remote  local                   LEVEL 3

Given the above fictional subcommand hierarchy, valid runtime uses would be (not an all inclusive list, and not including argument options per command for brevity and clarity):

$ git clone url
$ git push origin path
$ git add ref local
$ git commit message

Notice only one command per “level” may be used. You could not, for example, do $ git clone url push origin path

§Examples
 let app_m = App::new("git")
     .subcommand(SubCommand::with_name("clone"))
     .subcommand(SubCommand::with_name("push"))
     .subcommand(SubCommand::with_name("commit"))
     .get_matches();

match app_m.subcommand_name() {
    Some("clone")  => {}, // clone was used
    Some("push")   => {}, // push was used
    Some("commit") => {}, // commit was used
    _              => {}, // Either no subcommand or one not tested for...
}
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pub fn subcommand(&self) -> (&str, Option<&ArgMatches<'a>>)

This brings together ArgMatches::subcommand_matches and ArgMatches::subcommand_name by returning a tuple with both pieces of information.

§Examples
 let app_m = App::new("git")
     .subcommand(SubCommand::with_name("clone"))
     .subcommand(SubCommand::with_name("push"))
     .subcommand(SubCommand::with_name("commit"))
     .get_matches();

match app_m.subcommand() {
    ("clone",  Some(sub_m)) => {}, // clone was used
    ("push",   Some(sub_m)) => {}, // push was used
    ("commit", Some(sub_m)) => {}, // commit was used
    _                       => {}, // Either no subcommand or one not tested for...
}

Another useful scenario is when you want to support third party, or external, subcommands. In these cases you can’t know the subcommand name ahead of time, so use a variable instead with pattern matching!

// Assume there is an external subcommand named "subcmd"
let app_m = App::new("myprog")
    .setting(AppSettings::AllowExternalSubcommands)
    .get_matches_from(vec![
        "myprog", "subcmd", "--option", "value", "-fff", "--flag"
    ]);

// All trailing arguments will be stored under the subcommand's sub-matches using an empty
// string argument name
match app_m.subcommand() {
    (external, Some(sub_m)) => {
         let ext_args: Vec<&str> = sub_m.values_of("").unwrap().collect();
         assert_eq!(external, "subcmd");
         assert_eq!(ext_args, ["--option", "value", "-fff", "--flag"]);
    },
    _ => {},
}
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pub fn usage(&self) -> &str

Returns a string slice of the usage statement for the App or SubCommand

§Examples
let app_m = App::new("myprog")
    .subcommand(SubCommand::with_name("test"))
    .get_matches();

println!("{}", app_m.usage());

Trait Implementations§

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impl<'a> Clone for ArgMatches<'a>

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fn clone(&self) -> ArgMatches<'a>

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<'a> Debug for ArgMatches<'a>

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl<'a> Default for ArgMatches<'a>

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fn default() -> Self

Returns the “default value” for a type. Read more

Auto Trait Implementations§

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impl<'a> RefUnwindSafe for ArgMatches<'a>

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impl<'a> Send for ArgMatches<'a>

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impl<'a> Sync for ArgMatches<'a>

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impl<'a> Unpin for ArgMatches<'a>

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impl<'a> UnwindSafe for ArgMatches<'a>

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.