For quite a while, I've been wanting to add a method to sys::Map that does a "checked get", where if the key isn't mapped, then you get a exception. Something like this:

map[key] ?: throw Err("Key not mapped: $key")

Although we'd actually use containsKey to handle null values properly.

Definitely a useful method, but hard to come up with a good simple name. Current ideas:

• require
• obtain
• getRequired

Favorite so far is just call it require, but any other ideas?

From the list, getRequired has my vote.

I thought of something like

map[key, true] = value

to be consistent with other checked methods, but thinking about it, it actually makes no sense! So, err, forget about that!

You already have getOrAdd, how about getOrThrow ? Likes:

• Fits an existing pattern (xOrY)
• Starts with "get" so it goes near get and getOrAdd in the docs
• Very explicit about what it does, you probably don't have to check the docs to figure out the difference from a plain get.

I don't like require and obtain because they don't start with get and may not even make people think they simply get something if they've never seen them before.

getOrThrow

We have a winner! +1

getOrThrow returns a +1 for me!

votes := Str:Int[:] { def = 0 }
votes["getOrThrow"] += ["dobesv", "qualidafial", "SlimerDude", "StephenViles"].size

I'd expect that the new "checked get" method will throw an exception iff !containsKey(key). This is different from get(key) == null both for null values and for maps with a non-null def field.

I had considered getOrThrow as well - that is probably the most "semantic" choice. So +1.

I don't love getOrThrow, but can certainly live with that choice. It does nice effect of showing up in docs right next to get so makes it easily discoverable. I pushed this change