This class works around a limitation in C++03 whereby initializing a pass‐by‐value parameter of type bslmf::ArgumentType<N> from a MovableRef<bslmf::ArgumentType<N> > results in an ambiguous conversion sequence (i.e., MovableRef::operator T& vs. ArgumentType(MovableRef) are equally good conversions). Pass‐by‐value use cases (e.g., recording the value category of multiple function arguments) can use this class as a parameter type, instead, eliminating the ambiguity because MovableRef<AT> ‐> AT& ‐> ArgumentTypeByValue requires two user‐defined conversions and is therefore eliminated during overload resolution.

Synopsis

Declared in <bsltf_argumenttype.h>

template<int N>
class ArgumentTypeByValue
    : public ArgumentType<N>

Base Classes

Name

Description

ArgumentType<N>

This class template wraps an integer value and provides implicit conversion to, and explicit conversion from, int, while keeping track of copy and move operations. Its main purpose is for following an argument through a forwarding interface in test drivers. Each value of the template parameter N yields a unique type, enabling a test driver to distingusih them when calling through a function template interface, thereby avoiding ambiguities or accidental switching of arguments in the implementation of test‐class methods and constructors or in calls to methods and constructors of a class template under test. When an object of this type is copied or moved (via construction or assignment), the value returned by the copyMoveState accessor (the copy/move state), is updated for the target object and, in the case of a move, for the source object as well.

Member Functions

Name

Description

ArgumentTypeByValue [constructor]

Constructors

operator=

Assignment operators

copyMoveState

Return the copy/move state of this object.

movedFrom

Return MoveState::e_MOVED if this object was the source of a move construction or move‐assignment operation, MoveState::e_NOT_MOVED if it was not the source of a move operation, and MoveState::e_UNKNOWN if its copy/move state is not known. Note that converting the result to bool will yield true if this object was moved from and false otherwise. Note also that the value returned by this accessor may change if this object is subsequently the target of an assignment.

movedInto

Return MoveState::e_MOVED if this object was the target of a move construction or move‐assignment operation, MoveState::e_NOT_MOVED if it was not the target of a move operation, and MoveState::e_UNKNOWN if its copy/move state is not known. Note that converting the result to bool will yield true if this object was moved into and false otherwise. Note that the value returned by this accessor may change if this object is subsequently the source of a move operation or the target of an assignment.

reset

Set this object to the default‐constructed state.

set

Set this object to the specified value having the specified copy/move state. The behavior is undefined if the arguments would violate any class invariants, i.e., an invalid copy/move state, a value less than ‐1, or a moved‐from state with value other than ‐1.

operator int

Return the value of this object.

Non-Member Functions

Name

Description

copyMoveState

Return the copy/move state of the specified obj. This function is an ADL customization point used by CopyMoveState::get(obj).

debugprint

Print the specified value as a string. This is an ADL customization point.

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