Readonly-to-outside variable

[Baz via Digitalmars-d-learn]

On Tuesday, 28 April 2015 at 19:30:06 UTC, tcak wrote:
> Is there any way to define a variable or an attribute as 
> read-only without defining a getter function/method for it?
>
> Thoughts behind this question are:
> 1. For every reading, another function call process for CPU 
> while it could directly read the value from memory.
>
> 2. Repetition of same name for variable and getVariableName. 
> (Some might not agree with this but I like the code when it 
> looks nice.)

an quick attempt:

---
union ReadOnlyOutside(T)
{
     alias value this;
     private T _value;
     public const T value;
}
---

when you declare such a variable inside a struct or a class, the 
code located in another module won't be able to modify the value:

module1:

---
struct Foo
{
     ReadOnlyOutside!size_t roField;
}
---

module2:

void something(ref Foo foo)
{
     writeln(foo.roField); // OK
     writeln(foo.roField.value); // OK
     foo.roField = 1; // FAIL
     foo.roField.value = 1,// FAIL (because const).
     foo.roField._value = 1,// FAIL (because not visible).
}