Interested in D, spec confuses me.

[bubbasaur via Digitalmars-d]

On Tuesday, 2 February 2016 at 23:41:07 UTC, H. S. Teoh wrote:
> Now, the same argument applies if immutable was used in place 
> of const. However, the last line in main() illustrates why we 
> need const rather than immutable in this case: we actually 
> *want* to modify d.x in main(). We just don't want func2 to 
> touch anything. So we can't use immutable -- since immutable 
> means *nobody* can touch the data. So, const provides both the 
> guarantee that func2 won't touch the data, thus allowing the 
> aforementioned optimization, and also continues to let main() 
> mutate the data at its leisure.

Ok, but what would differ using immutable instead of const in 
your example (AS ARGUMENTS)?

See:

import std.stdio;

	struct Data { int x; }
	auto func1(Data* d) { return d.x; }
	auto func2(const(Data)* d) { return d.x; }
	auto func3(immutable(Data)* d) { return d.x; }	

	void main() {
		Data d;
		auto value1 = d.x*func1(&d) + d.x;
		auto value2 = d.x*func2(&d) + d.x;
		auto value3 = d.x*func3(cast(immutable)&d) + d.x;
		d.x++;
		writeln(d.x++);
	}

Functions 2 and 3 are acting in the same way and different from 
what you said I can change the d.x in main.

Bubba.