Authors CurseForge

"string library" is the terminology you want to be looking for.

Ah sorry, misunderstood :)

http://lua-users.org/wiki/ColonForMethodCall

You linked to the exact section of the Lua manual that goes into this:

Therefore, you can use the string functions in object-oriented style. For instance, string.byte(s, i) can be written as s:byte(i).

and from earlier in the manual

A call v:name(args) is syntactic sugar for v.name(v,args), except that v is evaluated only once. (sec 2.5.8)

That's the only substitution available for method calls:

s:byte(i) <-> string.byte(s,i)

Rearranging any of those identifiers into arbitrary order isn't legit. :-p

Quote from Farmbuyer

s:byte(i) <-> string.byte(s,i)

I'll expand on this a bit. Say you write the expression on the left:

s:byte(i)

The first thing Lua does (conceptually anyhow, the engine itself is smarter than all these steps I'm writing here) is to replace the "colon/method call" sugar with normal field access:

s.byte(s,i)

Next it replaces the "field access" sugar with actual key lookup:

s["byte"](s,i)

Now it tries to index 's' to find a key "byte"... except it can't, because strings don't have keys. If 's' were a table, it would actually look inside it, but since it's a string Lua skips the nonsensical lookup. The following steps are the same though.

Next it checks whether 's' has a metatable. (If the standard string library is loaded, then all strings are set to use the same metatable.)

Next it checks whether the metatable has an __index key. It does.

Next it checks whether __index refers to a function or to a table. In this case, it's a table, so the key lookup is repeated in that table. For strings, __index is set to point to the table called 'string' that contains all the library functions. So the final form is

string["byte"](s,i)

And again, that's more of a mental walkthrough, the Lua engine isn't doing all these teensy steps each time somebody writes str:lower().

Quote from Ketho

Besides, the reference manual is hard to read for noobs ><

It's definitely meant as a dry reference, not a friendly tutorial. If you have some spare change to drop, I highly recommend buying the 2nd edition of Programming in Lua. It's only available in print, not online, but the additional material and rewritten sections are a big improvement over the free online first edition.

The 'live demo' error is because string is not a method of string.

What you typed there s:string.sub(1,2)
would mean in loose english
"call the method 'string' of 's' passing itself (s) as a first argument"