C#是否有用于创建键/值对的简化语法?

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英文:

Does C# have a short-hand syntax for creating key/value pairs?

问题

I have a C# method declared like so:

public void Process<K, V>(params KeyValuePair<K, V>[] items)
{
    ...
}

Usage of this method looks kind of ugly; for example:

Process(
    new KeyValuePair("key", "value"),
    new KeyValuePair(123, Guid.NewGuid())
);

In Kotlin, you can create pairs using the to infix function; for example:

val pair1 = "key" to "value"
val pair2 = 123 to UUID.randomUUID()

So the equivalent method usage looks a little tidier; for example:

process("key" to "value", 123 to UUID.randomUUID())

C# doesn't have infix functions, but something nearly equivalent could be achieved with extension methods; for example:

public static KeyValuePair<K, V> To<K, V>(this K key, V value) where K : notnull
{
    return new KeyValuePair(key, value);
}

var pair1 = "key".To("value");
var pair2 = 123.To(Guid.NewGuid());

Process("key".To("value"), 123.To(Guid.NewGuid()));

That doesn't seem like the most elegant solution, so the other thing I was considering was that C# has dictionary initializer syntax; for example:

new Dictionary<object, object>()
{
    ["key"] = "value",
    [123] = Guid.NewGuid()
}

or

new Dictionary<object, object>()
{
    { "key", "value" },
    { 123, Guid.NewGuid() }
}

So I was wondering whether dictionary initializer syntax could be applied to a method parameter; for example:

Process({ ["key"] = "value", [123] = Guid.NewGuid() });

or

Process({{ "key", "value" }, { 123, Guid.NewGuid() }});

Questions

Is dictionary initializer syntax as a method parameter possible, or is it syntactic sugar provided by the compiler when using a dictionary?

Are there any other elegant ways to create params of KeyValuePair<K, V>?

英文:

I have a C# method declared like so:

public void Process&lt;K, V&gt;(params KeyValuePair&lt;K, V&gt;[] items)
{
    ...
}

Usage of this method looks kind of ugly; for example:

Process(
    new KeyValuePair(&quot;key&quot;, &quot;value&quot;),
    new KeyValuePair(123, Guid.NewGuid())
);

In Kotlin, you can create pairs using the to infix function; for example:

val pair1 = &quot;key&quot; to &quot;value&quot;
val pair2 = 123 to UUID.randomUUID()

So the equivalent method usage looks a little tidier; for example:

process(&quot;key&quot; to &quot;value&quot;, 123 to UUID.randomUUID())

C# doesn't have infix functions, but something nearly equivalent could be achieved with extension methods; for example:

public static KeyValuePair&lt;K, V&gt; To&lt;K, V&gt;(this K key, V value) where K : notnull
{
    return new KeyValuePair(key, value);
}

var pair1 = &quot;key&quot;.To(&quot;value&quot;);
var pair2 = 123.To(Guid.NewGuid());

Process(&quot;key&quot;.To(&quot;value&quot;), 123.To(Guid.NewGuid()));

That doesn't seem like the most elegant solution, so the other thing I was considering was that C# has dictionary initializer syntax; for example:

new Dictionary&lt;object, object&gt;()
{
    [&quot;key&quot;] = &quot;value&quot;,
    [123] = Guid.NewGuid()
}

or

new Dictionary&lt;object, object&gt;()
{
    { &quot;key&quot;, &quot;value&quot; },
    { 123, Guid.NewGuid() }
}

So I was wondering whether dictionary initializer syntax could be applied to a method parameter; for example:

Process({ [&quot;key&quot;] = &quot;value&quot;, [123] = Guid.NewGuid() });

or

Process({{ &quot;key&quot;, &quot;value&quot; }, { 123, Guid.NewGuid() }});

Questions

Is dictionary initializer syntax as a method parameter possible, or is it syntactic sugar provided by the compiler when using a dictionary?

Are there any other elegant ways to create params of KeyValuePair&lt;K, V&gt;?

答案1

得分: 9

这是目前(截至2023年,C# 11)C#原生支持的最佳方式。

正如您自己所写,C# 3引入了使用花括号的简化初始化,C# 6引入了命名参数初始化,而C# 9允许在可以推断出实例化类型时使用 new()

这意味着您可以执行以下操作:

// C# 3+
CallMethod(new Dictionary<string, string> { { "ka", "a" }, { "kb", "b" } });

// C# 6+
CallMethod(new Dictionary<string, string> { ["ka"] = "a", ["kb"] = "b" });

// C# 9+
CallMethod(new() { { "ka", "a" }, { "kb", "b" } });

如果您真的想要使用 params,减少一些按键次数的一种方法是使用 ValueTuple,类似于以下方式:

public static Dictionary<K, V> CallMethod<K, V>(params (K key, V value)[] values)
{
var dict = new Dictionary<K, V&gt();
foreach (var kvp in values)
{
dict[kvp.key] = kvp.value;
}
return dict;
}

然后您可以执行以下操作:

// C# 7+,返回类型被推断为 Dictionary<string, string>
CallMethod(("ka", "a"), ("kb", "b"));

[更新]

还有一个关于C# 12的提议更新,允许您使用以下语法:

// C# 12+ 提议
CallMethod(["ka": "a", "kb": "b"]);

英文:

This is currently (as of 2023, C# 11) the best you can get with C# out of the box.

As you wrote yourself, C# 3 introduced shorthand init using curly brackets, C# 6 introduced named parameters init, and C# 9 allows you to use new() when the instantiated type can be inferred.

Meaning that you can do:

// C# 3+
CallMethod(new Dictionary&lt;string, string&gt; { { &quot;ka&quot;, &quot;a&quot; }, { &quot;kb&quot;, &quot;b&quot; } });

// C# 6+
CallMethod(new Dictionary&lt;string, string&gt; { [&quot;ka&quot;] = &quot;a&quot;, [&quot;kb&quot;] = &quot;b&quot; });

// C# 9+
CallMethod(new() { { &quot;ka&quot;, &quot;a&quot; }, { &quot;kb&quot;, &quot;b&quot; } });

If you really want to use params, one way to reduce some keystrokes would be to use ValueTuples, something like

public static Dictionary&lt;K, V&gt; CallMethod&lt;K, V&gt;(params (K key, V value)[] values)
{
    var dict = new Dictionary&lt;K, V&gt;();
    foreach (var kvp in values)
    {
        dict[kvp.key] = kvp.value;
    }
    return dict;
}

and then you can do

// C# 7+, return type is inferred to be Dictionary&lt;string, string&gt;
CallMethod((&quot;ka&quot;, &quot;a&quot;), (&quot;kb&quot;, &quot;b&quot;));

[Update]

There is also a proposed update for collection literals in C#12 which would allow you to use the following syntax:

// C# 12+ proposal
CallMethod([&quot;ka&quot;: &quot;a&quot;, &quot;kb&quot;: &quot;b&quot;]);

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  • 本文由 发表于 2023年2月18日 19:33:50
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