Specify copy assignment operator for vec swizzles #678
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Even though we specify an assignment operator for `__writeable_swizzle__` like this: ``` template</*unspecified*/> const __writeable_swizzle__& operator=(const __writeable_swizzle__</*unspecified*/>& rhs) const ``` The compiler will not select this operator when the left-hand-side has the same type as the right-hand-side. (Even though the template constraints would allow such a selection.) Instead, the compiler will generate the default copy assignment operator and call that. Since the default copy assignment operator would not be correct (performing a shallow copy), the `__writeable_swizzle__` class must provide a user defined copy assignment operator. The copy assignment operator for `__const_swizzle__` was already deleted in the "constructors" section. It seemed better to move this to the "member functions" part of the specification, next to the specification for the copy assignment operator for `__writeable_swizzle__`.
nliber
requested changes
Feb 6, 2025
| [source] | ||
| ---- | ||
| const __writeable_swizzle__& | ||
| operator=(const __writeable_swizzle__& rhs) const |
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Why is this a const member function?
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Because the swizzle class is a "view". The assignment operator doesn't change the swizzle itself, it changes the underlying vec.
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It is still logically a non-const operation.
There is precedent in C++ for this, such as ostream_iterator::operator=(const T&) (as well as some of its other operators, like operator* and operator++).
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Discussed at the WG meeting 2025-02-06. span does similar things with operator[]. No change requested.
nliber
approved these changes
Feb 6, 2025
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Even though we specify an assignment operator for
__writeable_swizzle__like this:The compiler will not select this operator when the left-hand-side has the same type as the right-hand-side. (Even though the template constraints would allow such a selection.) Instead, the compiler will generate the default copy assignment operator and call that.
Since the default copy assignment operator would not be correct (performing a shallow copy), the
__writeable_swizzle__class must provide a user defined copy assignment operator.The copy assignment operator for
__const_swizzle__was already deleted in the "constructors" section. It seemed better to move this to the "member functions" part of the specification, next to the specification for the copy assignment operator for__writeable_swizzle__.