延迟模板字符串插值 [英] Deferred template string interpolation

问题描述

在C#中，有这样的字符串插值支持:

In C# there is a string interpolation support like this:

$"Constant with {Value}"

它将使用范围内变量 Value 格式化该字符串.

which will format this string using in-scope variable Value.

但是以下内容无法在当前的C#语法中进行编译.

But the following won't compile in current C# syntax.

说，我有一个静态的 Dictionary< string，string> 模板:

Say, I have a static Dictionary<string, string> of templates:

templates = new Dictionary<string, string>
{
    { "Key1", $"{Value1}" },
    { "Key2", $"Constant with {Value2}" }
}

然后在每次运行此方法时，我都要填写占位符:

And then on every run of this method I want to fill in the placeholders:

public IDictionary<string, string> FillTemplate(IDictionary<string, string> placeholderValues)
{
    return templates.ToDictionary(
        t => t.Key,
        t => string.FormatByNames(t.Value, placeholderValues));
}

在不执行那些占位符的Regex解析然后对该Regex进行替换回调的情况下是否可以实现?哪种方法最适合作为热路径?

Is it achievable without implementing Regex parsing of those placeholders and then a replace callback on that Regex? What are the most performant options that can suit this method as being a hot path?

例如，可以在Python中轻松实现:

For example, it is easily achievable in Python:

>>> templates = { "Key1": "{Value1}", "Key2": "Constant with {Value2}" }
>>> values = { "Value1": "1", "Value2": "example 2" }
>>> result = dict(((k, v.format(**values)) for k, v in templates.items()))
>>> result
{'Key2': 'Constant with example 2', 'Key1': '1'}
>>> values2 = { "Value1": "another", "Value2": "different" }
>>> result2 = dict(((k, v.format(**values2)) for k, v in templates.items()))
>>> result2
{'Key2': 'Constant with different', 'Key1': 'another'}

推荐答案

使用基于正则表达式进行替换的扩展方法，对于每个调用多个 Replace 调用，我获得了更快的速度值.

Using an extension method that does a substitution based on regular expressions, I get a good speed up over using multiple Replace calls for each value.

这是我的扩展方法，用于扩展大括号包围的变量:

Here is my extension method for expanding brace surrounded variables:

public static class ExpandExt {
    static Regex varPattern = new Regex(@"{(?<var>\w+)}", RegexOptions.Compiled);
    public static string Expand(this string src, Dictionary<string, string> vals) => varPattern.Replace(src, m => vals.TryGetValue(m.Groups[1].Value, out var v) ? v : m.Value);
}

这是使用它的示例代码:

And here is the sample code using it:

var ans = templates.ToDictionary(kv => kv.Key, kv => kv.Value.Expand(values));

在18个条目上使用 values 进行了10,000次以上的重复扩展，通常只有一次替换，与多个 String.Replace 调用相比，我得到的速度快3倍.

Over 10,000 repeating expansions with values at 18 entries and typically only one replacement, I get 3x faster than multiple String.Replace calls.

这篇关于延迟模板字符串插值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！