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

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.

Answer 2

If you don't have C#6 available in your project you can use Linq's .Aggregate():

    var str = "Her name is @name and she's @age years old";      var parameters = new Dictionary<string, object>();     parameters.Add("@name", "Lisa");     parameters.Add("@age", 10);      str = parameters.Aggregate(str, (current, parameter)=> current.Replace(parameter.Key, parameter.Value.ToString())); 

If you want something matching the specific syntax in the question you can put together a pretty simple class based on Aggregate:

public class StringFormatter{      public string Str {get;set;}      public Dictionary<string, object> Parameters {get;set;}      public StringFormatter(string p_str){         Str = p_str;         Parameters = new Dictionary<string, object>();     }      public void Add(string key, object val){         Parameters.Add(key, val);     }      public override string ToString(){         return Parameters.Aggregate(Str, (current, parameter)=> current.Replace(parameter.Key, parameter.Value.ToString()));     }  } 

Usable like:

var str = new StringFormatter("Her name is @name and she's @age years old"); str.Add("@name", "Lisa"); str.Add("@age", 10);  Console.WriteLine(str); 

Note that this is clean-looking code that's geared to being easy-to-understand over performance.