struct vs built-in type

[Jack Applegame via Digitalmars-d-learn]

Code:

import std.stdio;

struct Bar {
int payload;
alias payload this;
}
struct Foo {
private {
Bar m_bar;
int m_baz;
}
@property {
Bar bar() { return m_bar; }
void bar(Bar v) { m_bar = v; }
int baz() { return m_baz; }
void baz(int v) { m_baz = v; }
}
}

void main() {
Foo foo;
foo.bar += 4; // Compiles. Why?
foo.baz += 4; // Error: foo.baz() is not an lvalue
}

foo.baz() is not lvalue. It's true.
But foo.bar() is lvalue. Why? I expected the same error. This 
line has no effect, but the compiler does not issue even a 
warning.


DMD64 D Compiler v2.066.1. CentOS 7

Re: struct vs built-in type

[Daniel Kozák via Digitalmars-d-learn]

V Wed, 17 Dec 2014 07:57:24 +
Jack Applegame via Digitalmars-d-learn
digitalmars-d-learn@puremagic.com napsáno:

 Code:
 
 import std.stdio;
 
 struct Bar {
   int payload;
   alias payload this;
 }
 struct Foo {
   private {
   Bar m_bar;
   int m_baz;
   }
   @property {
   Bar bar() { return m_bar; }
   void bar(Bar v) { m_bar = v; }
   int baz() { return m_baz; }
   void baz(int v) { m_baz = v; }
   }
 }
 
 void main() {
   Foo foo;
   foo.bar += 4; // Compiles. Why?
   foo.baz += 4; // Error: foo.baz() is not an lvalue
 }
 
 foo.baz() is not lvalue. It's true.
 But foo.bar() is lvalue. Why? I expected the same error. This 
 line has no effect, but the compiler does not issue even a 
 warning.
 
 DMD64 D Compiler v2.066.1. CentOS 7

This is definitely compiler bug (if you print bar value it is still
zero). This should work only with ref by spec

module main;
import std.stdio;

struct Bar {
int payload;
alias payload this;
}
struct Foo {
private {
Bar m_bar;
int m_baz;
}
@property {
ref Bar bar() { return m_bar; }
void bar(Bar v) { m_bar = v; }
ref int baz() { return m_baz; }
void baz(int v) { m_baz = v; }
}
}

void main() {
Foo foo;
foo.bar += 4;
foo.baz += 4;
writeln(foo.bar);
}

Re: struct vs built-in type

[Rikki Cattermole via Digitalmars-d-learn]

On 17/12/2014 8:57 p.m., Jack Applegame wrote:

Code:

import std.stdio;

struct Bar {
 int payload;
 alias payload this;
}
struct Foo {
 private {
 Bar m_bar;
 int m_baz;
 }
 @property {
 Bar bar() { return m_bar; }
 void bar(Bar v) { m_bar = v; }
 int baz() { return m_baz; }
 void baz(int v) { m_baz = v; }
 }
}

void main() {
 Foo foo;
 foo.bar += 4; // Compiles. Why?
 foo.baz += 4; // Error: foo.baz() is not an lvalue
}

foo.baz() is not lvalue. It's true.
But foo.bar() is lvalue. Why? I expected the same error. This line has
no effect, but the compiler does not issue even a warning.

DMD64 D Compiler v2.066.1. CentOS 7


In this case, Bar can be treated as a reference type.
Where as a primitive type such as int is not. It is a literal.

Although I swear remembering this was a compiler bug and there was a 
discussion about it.


But just for thought:
struct Foo {
string text;
}

void main() {
Foo foo;
foo.doit;   

import std.stdio;
writeln(foo.text);
}


Given definition of doit:
void doit(Foo foo) {
foo.text = hi;  
}

It'll output a new line and thats it.
But for this:
void doit(ref Foo foo) {
foo.text = hi;  
}

It'll output hi.
In this case its explicitly provided by reference not as a literal.

Re: struct vs built-in type

[Jack Applegame via Digitalmars-d-learn]

On Wednesday, 17 December 2014 at 08:09:44 UTC, Daniel Kozák via 
Digitalmars-d-learn wrote:

This should work only with ref by spec

I totally agree.