[#BloombergLP-bslfmt-basic_format_arg-05]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslfmt.adoc[bslfmt]::xref:BloombergLP/bslfmt/basic_format_arg-0d.adoc[basic_format_arg]<xref:BloombergLP/bslfmt/basic_format_context.adoc[basic_format_context<t_OUT, t_CHAR>]>
:relfileprefix: ../../
:mrdocs:

STL‐compliant format argument holding a value for formatting.

== Synopsis

Declared in `<bslfmt_format_arg.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class t_OUT,
    class t_CHAR>
class xref:BloombergLP/bslfmt/basic_format_arg-0d.adoc[basic_format_arg]<xref:BloombergLP/bslfmt/basic_format_context.adoc[basic_format_context<t_OUT, t_CHAR>]>;
----

== Description

This class provides an STL‐compliant `basic_format_arg` which holds (by value for scalar and pointer types, by reference for user‐defined types). These types should not be constructed directly by the user.

== Types

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslfmt/basic_format_arg-05/handle.adoc[`handle`] 
| This class provides a type‐erased wrapper which holds a pointer to a user‐defined type and permits its formatting using the appropriate bsl::formatter type.
|===


== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslfmt/basic_format_arg-05/BoolType.adoc[`BoolType`] 
| Alias for the unspecified boolean conversion type used by this class.
| xref:BloombergLP/bslfmt/basic_format_arg-05/UnspecifiedBoolType.adoc[`UnspecifiedBoolType`] 
| Alias for `bsls::UnspecifiedBool` specialized on this class.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslfmt/basic_format_arg-05/2constructor.adoc[`basic_format_arg`]         [.small]#[constructor]#
| Create a `basic_format_arg` which holds a `bsl::monostate`.
| xref:BloombergLP/bslfmt/basic_format_arg-05/visit.adoc[`visit`] 
| Invoke `visitor` on the value contained by this object.
| xref:BloombergLP/bslfmt/basic_format_arg-05/2conversion.adoc[`operator BoolType`] 
| Return whether this object holds a value.
|===


== Friends

[cols="1,4"]
|===
| Name| Description
| `xref:BloombergLP/bslfmt/swap.adoc[BloombergLP::bslfmt::swap]`
| Exchange the values of the specified `lhs` and `rhs`.
| `xref:BloombergLP/bslfmt/Format_ArgUtil.adoc[BloombergLP::bslfmt::Format_ArgUtil]`
| Component‐private utilities for constructing format‐argument arrays.
|===


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