Creating global aliases/Type abbreviations: using global Directive

[bugproof]

There's no suitable alternative for typedef from C++. My proposition is to add using global directive that will allow defining global aliases:

so instead of writing this:

public class MyAliasForGenericType : GenericType<object>
{
// constructors...
...
}

we could write this:

using global MyAliasForGenericType = GenericType<object>;
using global MyNumber = int;

(we could define this in file like Aliases.cs or just below the type we're creating an alias for)

The problem with the first approach is that we can't implicitly convert from GenericType<object> to MyAliasForGenericType.

Today aliases can be used but only in the scope of the file, they're defined in. With using global it would be available everywhere. It would be great when access modifier could be set for an alias e.g. internal, or some attribute that controls the visibility.

internal using global MyAliasForGenericType = GenericType<object>;

or

using global internal MyAliasForGenericType = GenericType<object>;

or maybe something like

internal MyAliasForGenericType = GenericType<object>;
internal MyNumber = int;

similar to how F# does it https://fsharpforfunandprofit.com/posts/type-abbreviations/

[svick]

This looks like a duplicate of #1170, #410 and #259.

[YairHalberstadt]

Closing as duplicate of #1170, #410 and #259.