How can I use linq to initialize an array of repeated elements?

Question

At present, I'm using something like this to build a list of 10 objects:

myList = (from _ in Enumerable.Range(0, 10) select new MyObject {...}).toList()

This is based off my python background, where I'd write:

myList = [MyObject(...) for _ in range(10)]

Note that I want my list to contain 10 instances of my object, not the same instance 10 times.

Is this still a sensible way to do things in C#? Is there a cost to doing it this way over a simple for loop?

Answer 1

在这种情况下,Fluent API看起来更具可读性,但是不容易看到代码的意图:

var list = Enumerable.Range(0, 10).Select(_ => new MyObject()).ToList();

简单如果循环快速且易于理解,但它也隐藏了意图 - 创建10个项目的列表

List<MyObject> list = new List<MyObject>();
for (int i = 0; i < 10; i++)
     list.Add(new MyObject());

可读性最好的是构建器,它将描述您的意图

public class Builder<T>
    where T : new()
{
    public static IList<T> CreateListOfSize(int size)
    {
        List<T> list = new List<T>();
        for (int i = 0; i < size; i++)
            list.Add(new T());
        return list;
    }
}

用法:

var list = Builder<MyObject>.CreateListOfSize(10);

这个解决方案和简单的循环一样快,意图非常明确.同样在这种情况下,我们只需要编写最少量的代码.

Answer 2

你可以试试：

Enumerable.Range(0, 1000).Select(x => new MyObject()).ToArray();

Answer 3

就我个人而言，我认为Enumerable.Repeat缺少过载。一个方便的补充是这样的：

public static class EnumerableEx
{
    public static IEnumerable<T> Repeat<T>(int amt, Func<T> producer)
    {
        for(var i = 0; i < amt; ++i)
        {
            yield return producer();
        }
    }
}

所以你可以

EnumerableEx.Repeat(10, () => new object()) //.ToList()