C# Programming/Keywords/readonly

The readonly keyword is closely related to the const keyword at a glance, with the exception of allowing a variable with this modifier to be initialized in a constructor, along with being associated with a class instance (object) rather than the class itself.

The primary use for this keyword is to allow the variable to take on different values depending on which constructor was called, in case the class has many, while still ensuring the developer that it can never intentionally or unintentionally be changed in the code once the object has been created.

This is a sample usage, assumed to be in a class called SampleClass:

readonly string s;

    s = "Hello!";

C# Keywords
abstract as base bool break
byte case catch char checked
class const continue decimal default
delegate do double else enum
event explicit extern false finally
fixed float for foreach goto
if implicit in int interface
internal is lock long namespace
new null object operator out
override params private protected public
readonly ref return sbyte sealed
short sizeof stackalloc static string
struct switch this throw true
try typeof uint ulong unchecked
unsafe ushort using var virtual
void volatile while
Special C# Identifiers (Contextual Keywords)
add alias async await dynamic
get global nameof partial remove
set value when where yield
Contextual Keywords (Used in Queries)
ascending by descending equals from
group in into join let
on orderby select where