Should `Argv` be a part of the language base?

[ta0kira]

Supporting it requires code in base, and putting it in lib requires that that code is visible to all extensions.

This means at least the following:

• Any module with C++ extensions can read program args without using Argv from lib/util.

• Any module with C++ extensions can temporarily override Argv globally by putting a ProgramArgv on the stack during a function call. Although this in theory would be useful for testing purposes, this functionality can only be scoped to a C++ function.

  call () {
  SetArgv argv <- SetArgv$builder().add("foo").add("bar").build()
  // do some stuff with Argv$global() = { "foo", "bar" }
  }

  The example above cannot work because argv is a heap object and therefore cannot own a ThreadCapture instance. For this to actually work, the C++ extension would need to take a callback that gets executed while it has a ProgramArgv on the C++ stack.

  call () {
  WithArgv argv <- WithArgv$builder().add("foo").add("bar").build()
  \ argv.execute(myCallback)
  }

[ta0kira]

I've decided against this. The C++ version of Argv is a part of the base because it needs to be set in main, and lib/util is just a wrapper around the C++ functionality.

There is nothing special about that implementation, and it doesn't fit within the theme of the other categories in the base: All other built-ins either have syntax for literals (e.g., String, Bool) or are interfaces that types with literals need to implement.