究竟是什么标识了网站访问者？

Question

tretetex

Asked:2020-07-03 05:09:43 +0000 UTC2020-07-03 05:09:43 +0000 UTC 2020-07-03 05:09:43 +0000 UTC

制作通用方法

772

有一个通用类：

public struct Range<T>
{
    public T From { get; set; }
    public T To { get; set; }

    public bool HasValue(T value)
    {
        // Нужно написать проверку входа в диапазон
    }
}

T- 只能是数字 ( int, double) 或日期 ( DateTime)，也可以是Nullable.

有必要实现一个方法HasValue来检查它是否在从到value的范围内。FromTo

如果不使用强制转换和重载，这可能吗？

6 个回答

Voted

Qwertiy · Answer 1 · 2020-07-03T21:19:36Z

http://ideone.com/WBbU8d

using System;
using System.Collections.Generic;

public struct Range<T>
{
    public T From { get; set; }
    public T To { get; set; }

    public bool HasValue(T value)
    {
        return value != null
            && (From == null || Comparer<T>.Default.Compare(From, value) <= 0)
            && (To == null || Comparer<T>.Default.Compare(To, value) >= 0);
    }
}

并检查：

public class Test
{
    public static void Main()
    {
        var a = new Range <int> { From = 10, To = 16 };
        Console.WriteLine("var a = new Range <int> { From = 10, To = 16 };");
        Console.WriteLine(a.HasValue(0));
        Console.WriteLine(a.HasValue(15));
        Console.WriteLine(a.HasValue(17));
        Console.WriteLine();

        var b = new Range <int?> { From = 10, To = 16 };
        Console.WriteLine("var b = new Range <int?> { From = 10, To = 16 };");
        Console.WriteLine(b.HasValue(null));
        Console.WriteLine(b.HasValue(0));
        Console.WriteLine(b.HasValue(15));
        Console.WriteLine(b.HasValue(17));
        Console.WriteLine();

        var c = new Range <int?> { From = null, To = 16 };
        Console.WriteLine("var c = new Range <int?> { From = null, To = 16 };");
        Console.WriteLine(c.HasValue(null));
        Console.WriteLine(c.HasValue(0));
        Console.WriteLine(c.HasValue(15));
        Console.WriteLine(c.HasValue(17));
        Console.WriteLine();

        var d = new Range <int?> { From = 10, To = null };
        Console.WriteLine("var d = new Range <int?> { From = 10, To = null };");
        Console.WriteLine(d.HasValue(null));
        Console.WriteLine(d.HasValue(0));
        Console.WriteLine(d.HasValue(15));
        Console.WriteLine(d.HasValue(17));
        Console.WriteLine();

        var e = new Range <int?> { From = null, To = null };
        Console.WriteLine("var e = new Range <int?> { From = null, To = null };");
        Console.WriteLine(e.HasValue(null));
        Console.WriteLine(e.HasValue(0));
        Console.WriteLine(e.HasValue(15));
        Console.WriteLine(e.HasValue(17));
        Console.WriteLine();
    }
}

Alex Krass · Answer 2 · 2020-07-03T05:27:50Z

接口负责比较IComparable，你可以限制它们的类型。是的，那么您将无法将 Nullable 类型作为 T 传递。只能通过重载将它们与 From 和 To 进行比较HasValue(T? value)。我没有想到最好的解决方案。

public struct Range<T> where T : IComparable
{
    public T From
    {
        get;
        set;
    }
    public T To
    {
        get;
        set;
    }

    public bool HasValue(T value)
    {
        return value.CompareTo(From) >= 0 && value.CompareTo(To) <= 0;
    }

    public bool HasValue(T? value)
    {
        return value.HasValue && value.Value.CompareTo(From) >= 0 && value.Value.CompareTo(To) <= 0;
    }
}

UPD 带有 Nullable 检查的类（未测试，我不保证性能）

public struct Range<T> 
{
    public T From
    {
        get;
        set;
    }
    public T To
    {
        get;
        set;
    }

    public bool HasValue(T value) 
    {
        IComparable _from = null;
        IComparable _to = null;
        IComparable _value = null;

        if (From != null) 
        {
            _from = GetValue(From) as IComparable;
        }
        if (To != null)
        {
            _to = GetValue(To) as IComparable;
        }
        if (value != null)
        {
            _value = GetValue(value) as IComparable;
        }

        if (_value == null) throw new ArgumentNullException();

        bool checkFrom = false;
        if (_from == null || _from != null && _value.CompareTo(_from) >= 0) checkFrom = true;

        bool checkTo = false;
        if (_to == null || _to != null && _value.CompareTo(_to) <= 0) checkTo = true;

        return checkFrom && checkTo;
    }

    private T GetValue<T>(T t) { return t; }
    private T GetValue<T>(T? t) where T : struct { return t.Value; }

}

class Program
{
    static void Main(string[] args)
    {

        Console.WriteLine(new Range<int>() { From = -20, To = 20 }.HasValue(10)); //true
        Console.WriteLine(new Range<int>() { From = -20, To = 20 }.HasValue(-100)); //false
        Console.WriteLine(new Range<int>() { From = -20, To = 20 }.HasValue(100)); //false

        Console.WriteLine(new Range<int?>() { From = -20, To = 20 }.HasValue(10)); //true
        Console.WriteLine(new Range<int?>() { From = -20, To = 20 }.HasValue(-100)); //false
        Console.WriteLine(new Range<int?>() { From = -20, To = 20 }.HasValue(100)); //false
        Console.WriteLine(new Range<int?>() { From = null, To = 20 }.HasValue(10)); //true
        Console.WriteLine(new Range<int?>() { From = -20, To = null }.HasValue(10)); //true
        Console.WriteLine(new Range<int?>() { From = -20, To = null }.HasValue(-100)); //false

        Console.WriteLine(new Range<DateTime>() { From = DateTime.Now.AddDays(-5), To = DateTime.Now.AddDays(5) }.HasValue(DateTime.Now.AddDays(-2))); //true
        Console.WriteLine(new Range<DateTime>() { From = DateTime.Now.AddDays(-5), To = DateTime.Now.AddDays(5) }.HasValue(DateTime.Now.AddDays(-10))); //false
        Console.WriteLine(new Range<DateTime>() { From = DateTime.Now.AddDays(-5), To = DateTime.Now.AddDays(5) }.HasValue(DateTime.Now.AddDays(10))); //false
        Console.WriteLine(new Range<DateTime?>() { From = null, To = DateTime.Now.AddDays(5) }.HasValue(DateTime.Now.AddDays(-2))); //true
        Console.WriteLine(new Range<DateTime?>() { From = DateTime.Now.AddDays(-5), To = null }.HasValue(DateTime.Now.AddDays(-2))); //true
        Console.WriteLine(new Range<DateTime?>() { From = DateTime.Now.AddDays(-5), To = null }.HasValue(DateTime.Now.AddDays(-100))); //false

        Console.ReadLine();
    }
}

Alexander Petrov · Answer 3 · 2020-07-03T06:51:51Z

对于此类类型，您通常会创建一堆重载。例如，您可以看到方法Console.WriteLine。您可以这样做：创建许多结构/类来处理特定类型。为了不全部手动编写，可以使用T4代码生成。

在文件tt中我们写：

<#@ template debug="false" hostspecific="false" language="C#" #>
<#@ output extension=".cs" #>

using System;

namespace TestApp
{
    <# 
    var types = new string[] { "SByte", "Byte", "Char", "Int16", "UInt16", "Int32", "UInt32",
        "Int64", "UInt64", "Single", "Double", "Decimal", "DateTime", "DateTimeOffset" };

    foreach(var T in types) {
    #>
    public struct Range<#=T#>
    {
        public <#=T#> From { get; set; }
        public <#=T#> To { get; set; }

        public bool HasValue(<#=T#> value)
        {
            return value >= From && value <= To;
        }
    }
    public struct RangeNullable<#=T#>
    {
        public <#=T#>? From { get; set; }
        public <#=T#>? To { get; set; }

        public bool HasValue(<#=T#>? value)
        {
            return value >= From && value <= To;
        }
    }
    <#
        }
    #>
}

根据需要添加/减去类型。
编译后cs会生成一个包含很多结构的文件。

接下来，您将需要创建和使用明确指定类型的结构实例：

var range = new RangeInt32();
var range2 = new RangeNullableDateTime();

在原来它会是：

var range = new Range<int>();
var range2 = new Range<DateTime?>();

VladD · Answer 4 · 2020-07-03T20:28:20Z

另一个实现选项。

条件：要么该类型T不是Nullable，并且实现IComparable<Т>，要么它是一个类型T1?，并且它T1实现IComparable<Т1>。不幸的是在编译时没有检查。

class Range<T>
{
    // компаратор для не-nullable-случая
    static int CompareNonNullable<V>(V l, V r) where V : IComparable<V> => l.CompareTo(r);

    // компаратор для nullable-случая
    static int CompareNullable<V>(V? l, V? r) where V : struct, IComparable<V>
    {
        if (l == null)
            return r == null ? 0 : 1;
        else if (r == null)
            return -1;
        else return l.Value.CompareTo(r.Value);
    }

    static Range()
    {
        Type parameter = typeof(T);
        Type nullableBase = Nullable.GetUnderlyingType(typeof(T));

        Type underlying = nullableBase ?? parameter; // T или T1

        // проверка на IComparable
        var icomparable = typeof(IComparable<>).MakeGenericType(underlying);
        var hasInterface = underlying.GetInterfaces().Contains(icomparable);
        if (!hasInterface)
            throw new ArgumentException(
                "Type should implement IComparable generic interface");

        var methodName = (nullableBase == null) ? nameof(CompareNonNullable) :
                                                  nameof(CompareNullable);
        var rawMI = typeof(Range<T>).GetMethod(
                        methodName,
                        BindingFlags.Static | BindingFlags.NonPublic);
        var genericMI = rawMI.MakeGenericMethod(underlying);

        comparer = (Func<T, T, int>)Delegate.CreateDelegate(
                                        typeof(Func<T, T, int>), genericMI);
    }

    static Func<T, T, int> comparer;

    public Range(T from, T to)
    {
        From = from;
        To = to;
    }

    public bool Contains(T t) => comparer(From, t) <= 0 && comparer(t, To) <= 0;

    public T From { get; }
    public T To { get; }
}

像这样使用：

var intRange = new Range<int>(0, 5);
Console.WriteLine(intRange.Contains(5));

var dtRange = new Range<DateTime?>(DateTime.Now.AddDays(-1), null);
Console.WriteLine(dtRange.Contains(DateTime.Now));

Andrey Rygin · Answer 5 · 2020-07-11T01:25:23Z

Andrey Rygin

2020-07-11T01:25:23Z2020-07-11T01:25:23Z

可以通过扩展来完成：

public static class RangeExtensions
{
    public static bool HasValue<T>(this Range<T> range, T value, IComparer<T> comparer = null)
        where T : struct
    {
        comparer = comparer ?? Comparer<T>.Default;
        return comparer.Compare(value, range.From) >= 0 && comparer.Compare(value, range.To) <= 0;
    }

    public static bool HasValue<T>(this Range<T?> range, T? value, IComparer<T> comparer = null)
        where T : struct
    {
        comparer = comparer ?? Comparer<T>.Default;
        if (value == null || range.From == null || range.To == null)
        {
            return false;
        }

        return comparer.Compare(value.Value, range.From.Value) >= 0 && comparer.Compare(value.Value, range.To.Value) <= 0;
    }
}

如果 Range 是结构，则此方法存在潜在的性能问题 - 该结构将按值传递。如果 Range 将是一个类或者操作不频繁，那么试试这个。

1

Chloroform · Answer 6 · 2020-07-03T05:17:33Z

Chloroform

2020-07-03T05:17:33Z2020-07-03T05:17:33Z

实现是这样的：

public bool HasValue(T value)
{
    if (value == null)
        return false;
    return (value >= From) && (To >= value);
}

附言。第一次，我写错了。原来什么都不用带，因为。数字，DataTime我们可以比较。第一步是检查null，然后以通常的方式进行比较。

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