From Jason Turner

[temp.deduct.partial]

C++17 → C++20 3.5 KB 36 lines
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  1. tmp/tmpsw1soy8c/{from.md → to.md} +14 -17
tmp/tmpsw1soy8c/{from.md → to.md} RENAMED
@@ -20,21 +20,19 @@ as the parameter template.
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  The types used to determine the ordering depend on the context in which
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  the partial ordering is done:
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  - In the context of a function call, the types used are those function
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- parameter types for which the function call has arguments.[^7]
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  - In the context of a call to a conversion function, the return types of
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  the conversion function templates are used.
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- - In other contexts ([[temp.func.order]]) the function template’s
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- function type is used.
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  Each type nominated above from the parameter template and the
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  corresponding type from the argument template are used as the types of
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- `P` and `A`. If a particular `P` contains no *template-parameter*s that
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- participate in template argument deduction, that `P` is not used to
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- determine the ordering.
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  Before the partial ordering is done, certain transformations are
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  performed on the types used for partial ordering:
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  - If `P` is a reference type, `P` is replaced by the type referred to.
@@ -78,14 +76,13 @@ f(1, 2); // calls #3; non-variadic template #3 is more specialized
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  // than the variadic templates #1 and #2
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  ```
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  — *end example*]
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- If, for a given type, deduction succeeds in both directions (i.e., the
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- types are identical after the transformations above) and both `P` and
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- `A` were reference types (before being replaced with the type referred
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- to above):
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  - if the type from the argument template was an lvalue reference and the
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  type from the parameter template was not, the parameter type is not
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  considered to be at least as specialized as the argument type;
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  otherwise,
@@ -100,18 +97,18 @@ from `F` is at least as specialized as the type from `G`. `F` is *more
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  specialized than* `G` if `F` is at least as specialized as `G` and `G`
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  is not at least as specialized as `F`.
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  If, after considering the above, function template `F` is at least as
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  specialized as function template `G` and vice-versa, and if `G` has a
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- trailing parameter pack for which `F` does not have a corresponding
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- parameter, and if `F` does not have a trailing parameter pack, then `F`
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- is more specialized than `G`.
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- In most cases, all template parameters must have values in order for
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- deduction to succeed, but for partial ordering purposes a template
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- parameter may remain without a value provided it is not used in the
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- types being used for partial ordering.
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  [*Note 2*: A template parameter used in a non-deduced context is
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  considered used. — *end note*]
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  [*Example 2*:
 
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  The types used to determine the ordering depend on the context in which
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  the partial ordering is done:
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  - In the context of a function call, the types used are those function
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+ parameter types for which the function call has arguments.[^12]
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  - In the context of a call to a conversion function, the return types of
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  the conversion function templates are used.
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+ - In other contexts [[temp.func.order]] the function template’s function
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+ type is used.
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  Each type nominated above from the parameter template and the
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  corresponding type from the argument template are used as the types of
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+ `P` and `A`.
 
 
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  Before the partial ordering is done, certain transformations are
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  performed on the types used for partial ordering:
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  - If `P` is a reference type, `P` is replaced by the type referred to.
 
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  // than the variadic templates #1 and #2
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  ```
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  — *end example*]
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+ If, for a given type, the types are identical after the transformations
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+ above and both `P` and `A` were reference types (before being replaced
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+ with the type referred to above):
 
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  - if the type from the argument template was an lvalue reference and the
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  type from the parameter template was not, the parameter type is not
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  considered to be at least as specialized as the argument type;
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  otherwise,
 
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  specialized than* `G` if `F` is at least as specialized as `G` and `G`
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  is not at least as specialized as `F`.
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  If, after considering the above, function template `F` is at least as
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  specialized as function template `G` and vice-versa, and if `G` has a
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+ trailing function parameter pack for which `F` does not have a
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+ corresponding parameter, and if `F` does not have a trailing function
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+ parameter pack, then `F` is more specialized than `G`.
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+ In most cases, deduction fails if not all template parameters have
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+ values, but for partial ordering purposes a template parameter may
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+ remain without a value provided it is not used in the types being used
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+ for partial ordering.
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  [*Note 2*: A template parameter used in a non-deduced context is
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  considered used. — *end note*]
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  [*Example 2*: