On Tuesday, 5 September 2017 at 12:41:45 UTC, Computermatronic
wrote:
I find it very strange that this works, as a non-mixin template
should not be able to capture the context of where it was
instantiated. If you take the alias template parameters out it
behaves how it should (that is an error message saying this is
not accessible).
Computermatronic (and crimaniak and John Colvin):
The behavior is as should be expected and is part of the
definition of how templates' alias parameters are supposed to
work.
The error that occurs when you stop using an alias parameter
occurs because you're no longer forcing the capture of an
enclosing scope by passing in an alias parameter that requires
such a scope; not because the error should have occurred the
first time as well.
Circumstances where some "context" is captured include:
- template instantiations where an alias parameter requires a
context in order to resolve the parameter correctly [[the
instantiated function/struct/class will effectively become nested
within whichever scope is determined to be needed in order to
resolve the alias parameter -- whether the alias parameter is
needed, used, or not]]
- template instantiation of functions/structs/classes whose
enclosing templates were declared within a function/struct/class
[[the template instance's functions, structs, and classes will
effectively become nested within the function/struct/class that
the template was declared within -- whether the instantiated
function/struct/class's original declaration strictly implied a
need for an outer function/struct/class or not]]
- and --hrmm... it's 6:20 AM; I haven't yet slept for the night;
and I'm supposed to continue preparing to save myself from the
strongest hurricane ever seen in the Atlantic Ocean in a couple
hours, so I think that's where I'll end this partial list.
Some assorted details related to some miscellaneous capture
situations:
- https://dlang.org/spec/template.html#nested-templates
- https://dlang.org/spec/template.html#nested_template_limitation
- https://dlang.org/spec/template.html#aliasparameters
- https://dlang.org/spec/template.html#limitations
- https://dlang.org/spec/function.html#closures
