C# 数组初始化 - 使用非默认值
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原文地址: http://stackoverflow.com/questions/136836/
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C# Array initialization - with non-default value
提问by Rob
What is the slickest way to initialize an array of dynamic size in C# that you know of?
你知道的在 C# 中初始化动态大小数组的最巧妙方法是什么？
This is the best I could come up with
这是我能想到的最好的
private bool[] GetPageNumbersToLink(IPagedResult result)
{
if (result.TotalPages <= 9)
return new bool[result.TotalPages + 1].Select(b => true).ToArray();
...
采纳答案by Mark Cidade
回答by Matt Hamilton
Untested, but could you just do this?
未经测试，但你能这样做吗？
return result.Select(p => true).ToArray();
Skipping the "new bool[]" part?
跳过“new bool[]”部分？
回答by Matt Hamilton
I would actually suggest this:
我实际上建议这样做：
return Enumerable.Range(0, count).Select(x => true).ToArray();
This way you only allocate one array. This is essentially a more concise way to express:
这样你只分配一个数组。这本质上是一种更简洁的表达方式：
var array = new bool[count];
for(var i = 0; i < count; i++) {
array[i] = true;
}
return array;
回答by Neil Hewitt
EDIT: as a commenter pointed out, my original implementation didn't work. This version works but is rather un-slick being based around a for loop.
编辑：正如评论者指出的那样，我的原始实现不起作用。此版本有效，但基于 for 循环相当不流畅。
If you're willing to create an extension method, you could try this
如果你愿意创建一个扩展方法，你可以试试这个
public static T[] SetAllValues<T>(this T[] array, T value) where T : struct
{
for (int i = 0; i < array.Length; i++)
array[i] = value;
return array;
}
and then invoke it like this
然后像这样调用它
bool[] tenTrueBoolsInAnArray = new bool[10].SetAllValues(true);
As an alternative, if you're happy with having a class hanging around, you could try something like this
作为替代方案，如果你对有一个班级闲逛感到满意，你可以尝试这样的事情
public static class ArrayOf<T>
{
public static T[] Create(int size, T initialValue)
{
T[] array = (T[])Array.CreateInstance(typeof(T), size);
for (int i = 0; i < array.Length; i++)
array[i] = initialValue;
return array;
}
}
which you can invoke like
你可以像这样调用
bool[] tenTrueBoolsInAnArray = ArrayOf<bool>.Create(10, true);
Not sure which I prefer, although I do lurv extension methods lots and lots in general.
不确定我更喜欢哪个，尽管我通常做了很多 lurv 扩展方法。
回答by Nigel Touch
If by 'slickest' you mean fastest, I'm afraid that Enumerable.Repeatmay be 20x slower than a forloop. See http://dotnetperls.com/initialize-array:
如果“最流畅”是指最快，恐怕Enumerable.Repeat可能比for循环慢 20 倍。请参阅http://dotnetperls.com/initialize-array：
Initialize with for loop: 85 ms [much faster]
Initialize with Enumerable.Repeat: 1645 ms
So use Dotnetguy's SetAllValues() method.
所以使用 Dotnetguy 的 SetAllValues() 方法。
回答by Ohad Schneider
Many times you'd want to initialize different cells with different values:
很多时候你想用不同的值初始化不同的单元格：
public static void Init<T>(this T[] arr, Func<int, T> factory)
{
for (int i = 0; i < arr.Length; i++)
{
arr[i] = factory(i);
}
}
Or in the factory flavor:
或在工厂风味：
public static T[] GenerateInitializedArray<T>(int size, Func<int, T> factory)
{
var arr = new T[size];
for (int i = 0; i < arr.Length; i++)
{
arr[i] = factory(i);
}
return arr;
}
