In c# what the hell is the difference between const and readonly?  I looked this up today and:

Here’s what I found.

Constants (const):

• Are slightly less expensive to evealuate
• Are static by default
• Can be declared inside functions
• Have gotta have compile time value
• Are set at compile time inside assemblies that use them

Readonly (readonly) instance fields:

• Must have set value by the time constructor exits
• Are evaluated when instance is created

So I tend to use readonly fields if I ever think the constant will be referenced outside of my assembly.  Otherwise I’ll take the microsecond and use a const.