Explicit Slicing of std.container.Array

[Nordlöw]

Is there a reason why std.container.Array have to be explicitly 
sliced before being processed by range algorithms such as filter 
typically as

    import std.container: Array;
    Array!int a;
    foreach (e; a[].filter!"true") {}
?

Does memory allocation play a role?

I would like to see it be used in replace of D builtin arrays 
without any code changes.