First Draft: Static Single Assignment

[Peter C]

On Saturday, 6 December 2025 at 06:41:19 UTC, Peter C wrote:
>
> ...
> -- this is really how I want it to work --
>

What a true type‑level fixed annotation would look like if it 
were added to D:

// Passing fixed into functions

class Database { void bump() {} }

void useDb(fixed Database db)
{
     db.bump();  // interior mutation allowed
     db = new Database();  // error: cannot rebind fixed parameter
}

void main()
{
     fixed Database db = new Database();
     useDb(db);  // passes as fixed, guarantee preserved.
}

// -----------------------------------

// Returning fixed from functions

fixed Database makeDb()
{
     return new Database(); // initialized once, returned as fixed
}

void main()
{
     auto db = makeDb(); // inferred as fixed Database
     db = new Database(); // error: cannot rebind
     db.bump(); // interior mutation allowed
}

// ---------------------------