• Fangrui Song (16/16) Jan 28 2017 What cannot `string[][]` be implicitly converted to
• Yuxuan Shui (7/23) Jan 29 2017 immutable in D means array elements can't be modified by anyone

Fangrui Song <i maskray.me> writes:

What cannot `string[][]` be implicitly converted to 
`immutable(string[][])` as in `not_compilable`?



import std.stdio, std.range, std.algorithm, std.array;

void main() {
   immutable not_compilable = "a".split.map!(x => x.split).array;
   static immutable compilable0 = "a".split.map!(x => 
x.split).array;
   immutable compilable1 = "a".split.map!"a.split".array;
}



% dmd --version
DMD64 D Compiler v2.073.0
Copyright (c) 1999-2016 by Digital Mars written by Walter Bright

% dmd a.d
a.d(3): Error: cannot implicitly convert expression 
(array(map(split("a")))) of type string[][] to 
immutable(string[][])

Yuxuan Shui <yshuiv7 gmail.com> writes:

On Sunday, 29 January 2017 at 07:37:00 UTC, Fangrui Song wrote:
 What cannot `string[][]` be implicitly converted to 
 `immutable(string[][])` as in `not_compilable`?



 import std.stdio, std.range, std.algorithm, std.array;

 void main() {
   immutable not_compilable = "a".split.map!(x => x.split).array;
   static immutable compilable0 = "a".split.map!(x => 
 x.split).array;
   immutable compilable1 = "a".split.map!"a.split".array;
 }



 % dmd --version
 DMD64 D Compiler v2.073.0
 Copyright (c) 1999-2016 by Digital Mars written by Walter Bright

 % dmd a.d
 a.d(3): Error: cannot implicitly convert expression 
 (array(map(split("a")))) of type string[][] to 
 immutable(string[][])

immutable in D means array elements can't be modified by anyone 
(i.e. they will never change).

You cannot implicitly convert string[][] to immutable(string[][]) 
because the elements may still be modified through the original 
reference, which breaks the guarantee.

Correct way is to use .idup, or assumeUnique.