local type alias

[stephentoub]

From @juliusfriedman on July 19, 2016 14:40

Currently class declarations do not allow nested type aliasing e.g.

using MyTuple = System.Tuple<int, int>; even within a namespace declaration...

This declaration must normally be at the top of a file and precede all other using statements such as extern.

I propose that this restriction be lessened such that to allow one to use such aliases within their definitions to avoid redundant typing.

The only way this can be achieved now is to separate each class into it's own file and definitions of the class which fulfill the rule of the compiler by using partial or by declaring their own type which represents the type layout desired [thus reducing the use of a perfectly good structure such as Tuple simply due to the anonymity associated with such structures.].

Thank you for your time and consideration.

Copied from original issue: dotnet/corefx#10150

[alrz]

Probably the same as #218