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<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>?
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>();
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<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" } });
If you really want to use params, one way to reduce some keystrokes would be to use ValueTuples, something like
public static Dictionary<K, V> CallMethod<K, V>(params (K key, V value)[] values){var dict = new Dictionary<K, V>();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<string, string>CallMethod(("ka", "a"), ("kb", "b"));
[Update]
There is also a proposed update for collection literals in C#12 which would allow you to use the following syntax:
// C# 12+ proposalCallMethod(["ka": "a", "kb": "b"]);
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