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Nimrod中类似Ada的类型

nim-lang ada d

gour · 技术社区 · 12 年前

今天,我确实在D邮件列表中询问了是否可以以类似于Ada的示例的方式定义和使用自定义数据类型 wiki 第页:

type Day_type   is range    1 ..   31;
type Month_type is range    1 ..   12;
type Year_type  is range 1800 .. 2100;
type Hours is mod 24;
type Weekday is (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday); 


type Date is
   record
     Day   : Day_type;
     Month : Month_type;
     Year  : Year_type;
   end record;

subtype Working_Hours is Hours range 0 .. 12;
subtype Working_Day is Weekday range Monday .. Friday;
Work_Load: constant array(Working_Day) of Working_Hours 
   := (Friday => 6, Monday => 4, others => 10);

以及 reply 展示了如下内容:

import std.typecons;
import std.exception;

struct Limited(T, T lower, T upper)
{
    T _t;
    mixin Proxy!_t; //Limited acts as T (almost)
    invariant()
    {
        enforce(_t >= lower && _t <= upper);
    }
    this(T t)
    {
        _t = t;
    }
}

auto limited(T, T lower, T upper)(T init = T.init)
{
    return Limited!(T, lower, upper)(init);
}

unittest
{
    enum l = [-4,9];
    auto a = limited!(int, l[0], l[1])();
    foreach(i; l[0] .. l[1]+1)
    {
        a = i;
    }

    assertThrown({a = -5;}());
    assertThrown({a = 10;}());
}

这表明这是可能的,但可能错过了阿达的优雅。

现在,在最近读到关于Nimrod的文章后,我想知道它如何在有规定的情况下处理类似的任务,以确保相同的Ada类型的安全?

2 回复 | 直到 10 年前

zah 12 年前

Nimrod相当直接地支持这些:

type
  Day = range[1..31]
  Month = range[1..12]

  WeekDay = enum
    Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday

  WorkingDays = range[Monday..Friday]
  WorkingHours = range[0..12]

  WorkSchedule = array[WorkingDays, WorkingHours]

错误在编译时强制执行:

var x: Day
x = 40 # conversion from int literal(40) to Day is invalid

..或在运行时

var x: Day
var y = unknownInt() # let's say it returns 100

x = y # unhandled exception: value 100 out of range [EOutOfRange]

此外 distinct types 如果需要更强的类型安全性,则可以使用。

Community CDub 8 年前

此外,实例化变得更简单,使用

import std.traits;

/*! Instantiator for \c Limited. */
template limited(alias min, alias max, bool Exceptional = true)
    if (!is(CommonType!(typeof(min), typeof(max)) == void)) {
    auto limited(CommonType!(typeof(min), typeof(max)) value) {
        return Limited!(typeof(value), min, max)(value);
    }
}

看见 Instantiator Function for Bound template doesn't compile