difference between ReadOnly and Const?

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What is the difference between const and readonly?

are these interchangeable? can you show me code on how you would apply the two?

Duplicate of http://stackoverflow.com/questions/55984/what-is-the-difference-between-const-and-readonly — Eric Lippert, Jun 17 '10 at 20:48
And http://stackoverflow.com/questions/755685/c-static-readonly-vs-const — Eric Lippert, Jun 17 '10 at 20:49
And http://stackoverflow.com/questions/555534/when-if-ever-should-we-use-const — Eric Lippert, Jun 17 '10 at 20:50
And http://stackoverflow.com/questions/410723/is-there-a-difference-between-private-const-and-private-readonly-variables-in-c — Eric Lippert, Jun 17 '10 at 20:51
@Eric, the problem with such questions is that it is easier/faster to answer them than to search for dupes. But thumbs up for searching the dupes. — Lucero, Jun 17 '10 at 20:52
eric is the man! what a wonderful asset he is to the SOF community! thank you for your service eric — Alex Gordon, Jun 17 '10 at 21:02

score 3 · Accepted Answer · answered Jun 17 '10 at 20:48

No, they aren't.

A const field is literal value embedded in the assembly.
Only primitive values (strings and numbers) can be const, and they are evaluated at compile time.
When you reference a const field, the compiler embeds the literal value of the field. Therefore, if use use a const from another assembly, and the other assembly is recompiled with a different value, your assembly will only use the new value if you recompile it against the new version.

A readonly field is a normal field that cannot be changed outside the constructor.

answer this one: http://stackoverflow.com/questions/2624796/initialize-byte-array-from-a-portion-of-existing-byte-array-c — Alex Gordon, Jun 20 '10 at 20:23

score 3 · Answer 2 · answered Jun 17 '10 at 20:49

Const can't perform evaluations whereas readonly can on initialization. (ie you could read in a value for a readonly variable from a config file or based on some other parameter that is known at runtime, const can only be set to something known at compile time)

score 1 · Answer 3 · answered Jun 17 '10 at 20:52

A member of any type can be readonly. It simply means the member cannot be reassigned after the construction of the containing class; i.e., it cannot be set to a new object with the = operator. Mutable classes such as collections can still be modified with respect to their members; it's just that, if you have a readonly member that is a collection, it cannot be assigned to an entirely new collection after construction.

A const is not so different from a literal (like 5): it represents an unchanging value and thus only really makes sense in the context of specifying a value (as opposed to an object).

difference between ReadOnly and Const?

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