Std.BiMap.BiMap

type

This declaration introduces a public type.

What it does

A map that can be read from either side.

A currency code and its symbol, a user and their session, a variant and its

wire spelling: the pairing is the fact, and which side is the key depends on

which way the program happens to be going. An ordinary Map answers one of

those questions and makes the other a scan of everything it holds.

Keeping a second map by hand answers both, and is two writes that must not

come apart. This does that keeping, so a caller cannot forget half of it.

The part that is not symmetric with Map: a value can collide the way a key

can. Binding a to 1 and then b to 1 cannot leave both, because

looking up 1 would then have two answers and the reverse direction would

no longer be a map at all. The later binding wins and the earlier one is

removed entirely — insert can therefore make the map smaller, which is the

one surprise here and the reason insertChecked exists beside it.

Read the signature

• This declaration has no value signature because it introduces a type or trait.