[#boost-urls-grammar-squelch]
= xref:boost.adoc[boost]::xref:boost/urls.adoc[urls]::xref:boost/urls/grammar.adoc[grammar]::squelch
:relfileprefix: ../../../
:mrdocs:

Squelch the value of a rule

== Synopsis

Declared in `&lt;https://www.github.com/boostorg/url/blob/develop/include/boost/url/grammar/tuple_rule.hpp#L221[boost&sol;url&sol;grammar&sol;tuple&lowbar;rule&period;hpp]&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template&lt;xref:boost/urls/grammar/Rule.adoc[Rule] R&gt;
constexpr
&sol;&ast; implementation-defined &ast;&sol;
squelch(R const& r) noexcept;
----

== Description

This function returns a new rule which matches the specified rule, and converts its value type to `void`&period; This is useful for matching delimiters in a grammar, where the value for the delimiter is not needed&period;

== Value Type
[,cpp]
----
using value_type = void;
----
== Example 1
With `squelch`&colon;

[,cpp]
----
system::result< std::tuple< decode_view, core::string_view > > rv = parse(
    "www.example.com:443",
    tuple_rule(
        pct_encoded_rule(unreserved_chars + '-' + '.'),
        squelch( delim_rule( ':' ) ),
        token_rule( digit_chars ) ) );
----
== Example 2
Without `squelch`&colon;

[,cpp]
----
system::result< std::tuple< decode_view, core::string_view, core::string_view > > rv = parse(
    "www.example.com:443",
    tuple_rule(
        pct_encoded_rule(unreserved_chars + '-' + '.'),
        delim_rule( ':' ),
        token_rule( digit_chars ) ) );
----
== Return Value

The squelched rule

== Parameters

[cols=2]
|===
| Name
| Description
| *r*
| The rule to squelch
|===

== See Also

xref:boost/urls/grammar/delim_rule-0a.adoc[`delim&lowbar;rule`], xref:boost/urls/grammar/digit_chars.adoc[`digit&lowbar;chars`], xref:boost/urls/grammar/parse-09.adoc[`parse`], xref:boost/urls/grammar/tuple_rule.adoc[`tuple&lowbar;rule`], xref:boost/urls/grammar/token_rule.adoc[`token&lowbar;rule`], xref:boost/urls/decode_view.adoc[`decode&lowbar;view`], xref:boost/urls/pct_encoded_rule.adoc[`pct&lowbar;encoded&lowbar;rule`], xref:boost/urls/unreserved_chars.adoc[`unreserved&lowbar;chars`]&period;


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