# Enum regex_syntax::hir::HirKind

source · ```
pub enum HirKind {
Empty,
Literal(Literal),
Class(Class),
Anchor(Anchor),
WordBoundary(WordBoundary),
Repetition(Repetition),
Group(Group),
Concat(Vec<Hir>),
Alternation(Vec<Hir>),
}
```

## Expand description

The kind of an arbitrary `Hir`

expression.

## Variants§

### Empty

The empty regular expression, which matches everything, including the empty string.

### Literal(Literal)

A single literal character that matches exactly this character.

### Class(Class)

A single character class that matches any of the characters in the class. A class can either consist of Unicode scalar values as characters, or it can use bytes.

### Anchor(Anchor)

An anchor assertion. An anchor assertion match always has zero length.

### WordBoundary(WordBoundary)

A word boundary assertion, which may or may not be Unicode aware. A word boundary assertion match always has zero length.

### Repetition(Repetition)

A repetition operation applied to a child expression.

### Group(Group)

A possibly capturing group, which contains a child expression.

### Concat(Vec<Hir>)

A concatenation of expressions. A concatenation always has at least two child expressions.

A concatenation matches only if each of its child expression matches one after the other.

### Alternation(Vec<Hir>)

An alternation of expressions. An alternation always has at least two child expressions.

An alternation matches only if at least one of its child expression matches. If multiple expressions match, then the leftmost is preferred.

## Implementations§

source§### impl HirKind

### impl HirKind

source#### pub fn is_empty(&self) -> bool

#### pub fn is_empty(&self) -> bool

Return true if and only if this HIR is the empty regular expression.

Note that this is not defined inductively. That is, it only tests if
this kind is the `Empty`

variant. To get the inductive definition,
use the `is_match_empty`

method on `Hir`

.

source#### pub fn has_subexprs(&self) -> bool

#### pub fn has_subexprs(&self) -> bool

Returns true if and only if this kind has any (including possibly empty) subexpressions.