Szathmáry László honlapja @ DEIK | DLang / mutable slice -> immutable slice

Let's see how to convert a mutable slice to an immutable slice.

With copy

(1) copy

import std.stdio;
import std.conv;

void main()
{
int[] slice = [1, 2, 3];
auto immSlice = to!(immutable int[])(slice);

slice[0] = 10;

writeln(slice); // [10, 2, 3]
writeln(immSlice); // [1, 2, 3]
}

Notes:

Here, we make a copy of slice. The result, immSlice will be an immutable copy of the original slice.
Notice the syntax. In "to!(immutable int[])(slice)", (slice) at the end must be between parentheses.

With transformation

(2) transformation

import std.stdio;
import std.exception; // assumeUnique()

void main()
{
int[] slice = [1, 2, 3];

auto immSlice = assumeUnique(slice);

writeln(slice is null); // true
writeln(immSlice); // [1, 2, 3]

// immSlice[0] = 10; // error
}

Notes:

Here, no copy operation happens. immSlice will be an immutable view on the original slice.
assumeUnique(slice) sets the reference slice to null. Thus, after the transformation, the slice cannot be changed via the reference slice. This is done to avoid this kind of error.
After the transformation, immSlice is an immutable slice.