pub struct Hir { /* private fields */ }
Expand description

A high-level intermediate representation (HIR) for a regular expression.

The HIR of a regular expression represents an intermediate step between its abstract syntax (a structured description of the concrete syntax) and compiled byte codes. The purpose of HIR is to make regular expressions easier to analyze. In particular, the AST is much more complex than the HIR. For example, while an AST supports arbitrarily nested character classes, the HIR will flatten all nested classes into a single set. The HIR will also “compile away” every flag present in the concrete syntax. For example, users of HIR expressions never need to worry about case folding; it is handled automatically by the translator (e.g., by translating (?i)A to [aA]).

If the HIR was produced by a translator that disallows invalid UTF-8, then the HIR is guaranteed to match UTF-8 exclusively.

This type defines its own destructor that uses constant stack space and heap space proportional to the size of the HIR.

The specific type of an HIR expression can be accessed via its kind or into_kind methods. This extra level of indirection exists for two reasons:

  1. Construction of an HIR expression must use the constructor methods on this Hir type instead of building the HirKind values directly. This permits construction to enforce invariants like “concatenations always consist of two or more sub-expressions.”
  2. Every HIR expression contains attributes that are defined inductively, and can be computed cheaply during the construction process. For example, one such attribute is whether the expression must match at the beginning of the text.

Also, an Hir’s fmt::Display implementation prints an HIR as a regular expression pattern string, and uses constant stack space and heap space proportional to the size of the Hir.

Implementations

Returns a reference to the underlying HIR kind.

Consumes ownership of this HIR expression and returns its underlying HirKind.

Returns an empty HIR expression.

An empty HIR expression always matches, including the empty string.

Creates a literal HIR expression.

If the given literal has a Byte variant with an ASCII byte, then this method panics. This enforces the invariant that Byte variants are only used to express matching of invalid UTF-8.

Creates a class HIR expression.

Creates an anchor assertion HIR expression.

Creates a word boundary assertion HIR expression.

Creates a repetition HIR expression.

Creates a group HIR expression.

Returns the concatenation of the given expressions.

This flattens the concatenation as appropriate.

Returns the alternation of the given expressions.

This flattens the alternation as appropriate.

Build an HIR expression for ..

A . expression matches any character except for \n. To build an expression that matches any character, including \n, use the any method.

If bytes is true, then this assumes characters are limited to a single byte.

Build an HIR expression for (?s)..

A (?s). expression matches any character, including \n. To build an expression that matches any character except for \n, then use the dot method.

If bytes is true, then this assumes characters are limited to a single byte.

Return true if and only if this HIR will always match valid UTF-8.

When this returns false, then it is possible for this HIR expression to match invalid UTF-8.

Returns true if and only if this entire HIR expression is made up of zero-width assertions.

This includes expressions like ^$\b\A\z and even ((\b)+())*^, but not ^a.

Return true if and only if this HIR is required to match from the beginning of text. This includes expressions like ^foo, ^(foo|bar), ^foo|^bar but not ^foo|bar.

Return true if and only if this HIR is required to match at the end of text. This includes expressions like foo$, (foo|bar)$, foo$|bar$ but not foo$|bar.

Return true if and only if this HIR is required to match from the beginning of text or the beginning of a line. This includes expressions like ^foo, (?m)^foo, ^(foo|bar), ^(foo|bar), (?m)^foo|^bar but not ^foo|bar or (?m)^foo|bar.

Note that if is_anchored_start is true, then is_line_anchored_start will also be true. The reverse implication is not true. For example, (?m)^foo is line anchored, but not is_anchored_start.

Return true if and only if this HIR is required to match at the end of text or the end of a line. This includes expressions like foo$, (?m)foo$, (foo|bar)$, (?m)(foo|bar)$, foo$|bar$, (?m)(foo|bar)$, but not foo$|bar or (?m)foo$|bar.

Note that if is_anchored_end is true, then is_line_anchored_end will also be true. The reverse implication is not true. For example, (?m)foo$ is line anchored, but not is_anchored_end.

Return true if and only if this HIR contains any sub-expression that is required to match at the beginning of text. Specifically, this returns true if the ^ symbol (when multiline mode is disabled) or the \A escape appear anywhere in the regex.

Return true if and only if this HIR contains any sub-expression that is required to match at the end of text. Specifically, this returns true if the $ symbol (when multiline mode is disabled) or the \z escape appear anywhere in the regex.

Return true if and only if the empty string is part of the language matched by this regular expression.

This includes a*, a?b*, a{0}, (), ()+, ^$, a|b?, \B, but not a, a+ or \b.

Return true if and only if this HIR is a simple literal. This is only true when this HIR expression is either itself a Literal or a concatenation of only Literals.

For example, f and foo are literals, but f+, (foo), foo(), `` are not (even though that contain sub-expressions that are literals).

Return true if and only if this HIR is either a simple literal or an alternation of simple literals. This is only true when this HIR expression is either itself a Literal or a concatenation of only Literals or an alternation of only Literals.

For example, f, foo, a|b|c, and foo|bar|baz are alternation literals, but f+, (foo), foo(), `` are not (even though that contain sub-expressions that are literals).

Trait Implementations

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

Print a display representation of this Hir.

The result of this is a valid regular expression pattern string.

This implementation uses constant stack space and heap space proportional to the size of the Hir.

Formats the value using the given formatter. Read more

A custom Drop impl is used for HirKind such that it uses constant stack space but heap space proportional to the depth of the total Hir.

Executes the destructor for this type. Read more

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

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

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into)

Uses borrowed data to replace owned data, usually by cloning. Read more

Converts the given value to a String. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.