On 1/12/12 1:17 PM, Marijn Haverbeke wrote:
Note the phrase "aren't known at compile time." That reads as if bounded types
offer runtime polymorphism. (They don't, do they?)
They do.
They do and they don't. I think what Graham means is that if I write a
function:
inter X { ... }
fn foo<T:X>(x: [T]) { ... }
The function foo() is compiled without knowledge of what T is, but it
can only be applied to one T at a time. In other words, the list is
always a list of values of one type (i.e., T). This is polymorphic but
in a somewhat more limited sense than a C++ object.
However, we also allow values to be *cast* to the interface type, so you
can write:
fn foo(x: [X]) { ... }
and now the function foo() accepts a list whose contents may be of many
different types, all of which support the interface X.
Niko
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