Principled method of lookup-or-insert in associative arrays?

[Pelle Månsson]

On 11/20/2010 05:09 PM, spir wrote:
> ???
> backdoor and s do not denote the same element. One is a mutable array, the other is immutable. Why should changing backdoor affect s? Whether backdoor and chars denote the same array depends on whether "=" copies or not dyn arrays. But from immutable string to mutable array, there must be a copy (read: dup).

Must also be a copy the other way. Secret heap allocations are not fun.

> Anyway, the most annoying issue is not about assignments inside a given scope, but parameter passing (including implicit ones like in Andrei's example of foreach).
> 	void f (char[] chars) {}
> 	void g (string str) {}
> 	...
> 	string str = "abc";
> 	char[] chars = "abc".dup;
> 	f(str);
> 	g(chars);
> __trials__.d(30): Error: function __trials__.f (char[] chars) is not callable using argument types (string)
> __trials__.d(31): Error: function __trials__.g (string str) is not callable using argument types (char[])
> 	...
> 	f(str.dup);	// ok
> 	g(chars.idup);	// ditto
>

I do not understand the alternative.

>
> By the way, why isn't the definition of string immutable(char[]), instead of immutable(char)[]?
>

string s = "abc";
s = "bde"; // fails with immutable(char[]), rightly so.