[译]C# 7系列，Part 10: Span&lt；T&gt； and universal memory management Span&lt；T&gt；和统一内存管理「建议收藏」

// 使用隐式操作 Span<char>(char[])。
Span<char> span1 = new char[] { 's', 'p', 'a', 'n' };

// 使用stackalloc。
Span<byte> span2 = stackalloc byte[50];

// 使用构造函数。
IntPtr array = new IntPtr();
Span<int> span3 = new Span<int>(array.ToPointer(), 1);

// 创建一个实例：
Span<char> span = new char[] { 's', 'p', 'a', 'n' };
// 访问第一个元素的引用。
ref char first = ref span[0];
// 给引用设置一个新的值。
first = 'S';
// 新的字符串"Span".
Console.WriteLine(span.ToArray());

// 返回一个新的span从索引1到末尾.
// 得到"pan"。
Span<char> span2 = span.Slice(1);
Console.WriteLine(span2.ToArray());

private static void Main(string[] args)
{
    string test = "   Hello, World! ";
    Console.WriteLine(Trim(test.ToCharArray()).ToArray());
}

private static Span<char> Trim(Span<char> source)
{
    if (source.IsEmpty)
    {
        return source;
    }

    int start = 0, end = source.Length - 1;
    char startChar = source[start], endChar = source[end];

    while ((start < end) && (startChar == ' ' || endChar == ' '))
    {
        if (startChar == ' ')
        {
            start++;
        }

        if (endChar == ' ')
        {
            end—;
        }

        startChar = source[start];
        endChar = source[end];
    }

    return source.Slice(start, end - start + 1);
}

private static async Task Main(string[] args)
{
    Memory<byte> memory = new Memory<byte>(new byte[50]);
    int count = await ReadFromUrlAsync("https://www.microsoft.com", memory).ConfigureAwait(false);
    Console.WriteLine("Bytes written: {0}", count);
}

private static async ValueTask<int> ReadFromUrlAsync(string url, Memory<byte> memory)
{
    using (HttpClient client = new HttpClient())
    {
        Stream stream = await client.GetStreamAsync(new Uri(url)).ConfigureAwait(false);
        return await stream.ReadAsync(memory).ConfigureAwait(false);
    }
}

private static void Main(string[] args)
{
    // Implicit operator ReadOnlySpan(string).
    ReadOnlySpan<char> test = "   Hello, World! ";
    Console.WriteLine(Trim(test).ToArray());
}

private static ReadOnlySpan<char> Trim(ReadOnlySpan<char> source)
{
    if (source.IsEmpty)
    {
        return source;
    }

    int start = 0, end = source.Length - 1;
    char startChar = source[start], endChar = source[end];

    while ((start < end) && (startChar == ' ' || endChar == ' '))
    {
        if (startChar == ' ')
     {
            start++;
        }

        if (endChar == ' ')
        {
            end—;
        }

        startChar = source[start];
        endChar = source[end];
    }

    return source.Slice(start, end - start + 1);
}

private static void Main(string[] args)
{
    string source = "span like types are awesome!";
    // source.ToMemory() 转换变量 source 从字符串类型为 ReadOnlyMemory<char>,
    // and MemoryMarshal.AsMemory 转换 ReadOnlyMemory<char> 为 Memory<char>
    // 这样你就可以修改元素了。
    TitleCase(MemoryMarshal.AsMemory(source.AsMemory()));
    // 得到 "Span like types are awesome!";
    Console.WriteLine(source);
}

private static void TitleCase(Memory<char> memory)
{
    if (memory.IsEmpty)
    {
        return;
    }

    ref char first = ref memory.Span[0];
    if (first >= 'a' && first <= 'z')
    {
        first = (char)(first - 32);
    }
}