Re: Create custom data types

[Dennis Ritchie via Digitalmars-d-learn]

On Wednesday, 29 April 2015 at 21:49:08 UTC, Ali Çehreli wrote:
On 04/29/2015 12:53 PM, Dennis Ritchie wrote:
On Wednesday, 29 April 2015 at 17:52:27 UTC, Ali Çehreli wrote:
It should be easy to make a template of it. (I really think 
it should
already be in Phobos. :) )

Where can I find documentation on this subject?

Once a piece of code works for a particular type or value, it 
is easy to convert it to a template by moving the type and the 
value to the template parameter list and replace all 
occurrences of those with template parameters:

- int -> T

- -32_000 -> minValue

- 32_000 -> maxValue

Here it is:

import std.exception;

struct CustomInteger(T, T minValue, T maxValue)
{
    T value_;

    alias value this;

    @property T value() const
    {
        enforce((value_ >= minValue) &&
                (value_ <= maxValue));

        return value_;
    }

    @property void value(T v)
    {
        value_ = v;
    }
}

unittest
{
    alias Balance = CustomInteger!(int, -32_000, 32_000);

    auto b = Balance(42);
    assert(b == 42);

    b = 40_000;

    void foo(int) {}
    assertThrown(foo(b));
}

void main()
{}

Ali

Thanks. And how can I stop all attempts to perform actions 
arifmiticheskih the type int? Ie action to "t += b;" suppressed 
to compile.

-----
import std.exception, std.stdio;

struct CustomInteger(T, T minValue, T maxValue)
{
        T value_;
        
        alias value this;
        
        @property T value() const
        {
                enforce((value_ >= minValue) &&
                        (value_ <= maxValue));
                
                return value_;
        }
        
        @property void value(T v)
        {
                value_ = v;
        }
}

void main()
{
        alias Balance = CustomInteger!(int, -32_000, 32_000);
        
        auto b = Balance(42);

        // b += 5; // Error: 'b += 5' is not a scalar,
        // it is a CustomInteger!(int, -32000, 32000)

        int t = 4;

        t += b; // OK

        writeln(b); // prints 46
}