Does C# 6.0's String interpolation rely on Reflection?

Question

Short and simple. Does the new string interpolation in C# 6.0 rely on reflection? I.e. does

string myStr = $"Hi {name}, how are you?";

use reflection at runtime to find the variable "name" and its value?

Answer 1

No. It doesn't. It is completely based on compile-time evaluation.

You can see that with this TryRoslyn example that compiles and decompiles this:

int name = 4;
string myStr = $"Hi {name}, how are you?";

Into this:

int num = 4;
string.Format("Hi {0}, how are you?", num);

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string interpolation also supports using IFormattable as the result so (again using TryRoslyn) this:

int name = 4;
IFormattable myStr = $"Hi {name}, how are you?";

Turns into this:

int num = 4;
FormattableStringFactory.Create("Hi {0}, how are you?", new object[] { num });

Answer 2

This article explains that it's compile-time based (and internally calls string.Format(). A quote:

String interpolation is transformed at compile time to invoke an equivalent string.Format call. This leaves in place support for localization as before (though still with composite format strings) and doesn’t introduce any post compile injection of code via strings.