Is there a "String.Format" that can accept named input parameters instead of index placeholders?

Question

This is what I know

str = String.Format("Her name is {0} and she's {1} years old", "Lisa", "10");

But I want something like

str = String("Her name is @name and she's @age years old");
str.addParameter(@name, "Lisa");
str.addParameter(@age, 10);

Answer 1

In C# 6 you can use string interpolation:

string name = "Lisa";
int age = 20;
string str = $"Her name is {name} and she's {age} years old";

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As Doug Clutter mentioned in his comment, string interpolation also supports format string. It's possible to change the format by specifying it after a colon. The following example will output a number with a comma and 2 decimal places:

var str = $"Your account balance is {balance:N2}"

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As Bas mentioned in his answer, string interpolation doesn't support template string. Actually, it has no built in support for that. Fortunately it exists in some great libraries.

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SmartFormat.NET for example has support for named placeholder:

Smart.Format("{Name} from {Address.City}, {Address.State}", user)

// The user object should at least be like that 

public class User
{
    public string Name { get; set; }
    public Address Address { get; set; }
}

public class Address
{
    public string City { get; set; }
    public string State { get; set; }
}

It is available on NuGet.

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Mustache is also a great solution. Bas has described its pros well in his answer.