Create speclet for lambda discard parameters #2901
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| ## Detailed design | ||
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| In a lambda or delegate declaration with more than one parameter named `_`, those parameters are discard parameters. |
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This specification does not describe the scoping implications. Is there any hiding? #Closed
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| ## Detailed design | ||
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| In a lambda or delegate declaration with more than one parameter named `_`, those parameters are discard parameters. |
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delegate declaration [](start = 15, length = 20)
Did you really mean "delegate declaration", that is, a declaration of a delegate type? #Closed
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| In a lambda or delegate declaration with more than one parameter named `_`, those parameters are discard parameters. | ||
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| Discard parameters are not in scope in the body of the lambda or delegate. So they cannot be accessed. |
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parameters are not in scope [](start = 8, length = 27)
Can you pose this as a set of changes to the language specification, e.g. name lookup? #Resolved
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I took a stab at this:
In the section on method parameters and scopes, I would say that discard parameters do not add any names in scope.
In the section on corresponding parameters, I would say that named arguments do not correspond to discard parameters. #Resolved
proposals/discard-parameters.md
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| ## Detailed design | ||
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| In a parameter list with more than one parameter named `_`, such parameters are discard parameters. |
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more than one parameter named
_[](start = 24, length = 34)
The spec currently makes this an error. What spec changes are proposed to make it not be an error.
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"It is an error for two members of a method declaration space to have the same name." (method parameters).
I'll update speclet to say that discard parameters don't have a name (so the above rule doesn't apply).
proposals/discard-parameters.md
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| In a parameter list with more than one parameter named `_`, such parameters are discard parameters. | ||
| Note: if a single parameter is named `_` then it is a regular parameter for backwards compatibility reasons. | ||
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| Discard parameters do not introduce any names to any scopes. |
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do not introduce any names to any scopes [](start = 19, length = 40)
What name lookup changes are proposed to implement this intent in the specification?
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Which section of the spec do you refer to for "name lookup"?
I think I'm proposing that we don't change name lookup, but rather we change what names are added to what scopes.
"Names are introduced into this declaration space by the type parameter list and the formal parameter list of the method and by local variable declarations in the block of the method." (method parameters) would be affected by the rule that discard parameters don't introduce a name in any scope.
| In the parameter list of a lambda or anonymous method with more than one parameter named `_`, such parameters are discard parameters. | ||
| Note: if a single parameter is named `_` then it is a regular parameter for backwards compatibility reasons. | ||
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| Discard parameters do not introduce any names to any scopes. |
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introduce any names to any scopes [](start = 26, length = 33)
Please identify the intended change to 8.7 Scopes.
You will need to modify the name lookup rules to cause this intent to be reified in the specification. For example, we have the following text in ECMA's 12.7.3 Simple Names (giving the meaning of a simple name as an expression):
- If
Kis zero and the simple-name appears within a block and if the block’s (or an enclosing block’s) local variable declaration space (§8.3) contains a local variable, parameter or constant with nameI, then the simple-name refers to that local variable, parameter or constant and is classified as a variable or value.
Note that the discard parameter is in the declaration space by 8.3, and is a parameter named _ (see line 16 above), so without a change to the quoted paragraph it is indeed found during name lookup. Please identify the intended changes to the specification. #Resolved
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@gafter I'll go ahead and merge. Feel free to provide further comments. I'll address separately. Thanks |
Relates to championed issue #111