Add string_map buildfile value type

This exposes the std::map<std::string,std::string> type to buildfiles.

New functions:

  $size(<string-map>)
  $keys(<string-map>)

Subscript can be used to lookup a value by key. The result is [null] if
there is no value associated with the specified key. For example:

map = [string_map] a@1 b@2 c@3

b = ($map[b])  # 2

if ($map[z] == [null])
  ...

Note that append (+=) is overriding (like std::map::insert_or_assign())
while prepend (=+) is not (like std::map::insert()). In a sense, whatever
appears last (from left to right) is kept, which is consistent with what
we expect to happen when specifying the same key repeatedly in a literal
representation. For example:

map = [string_map] a@0 b@2 a@1  # a@1 b@2
map += b@0 c@3                  # a@1 b@0 c@3
map =+ b@1 d@4                  # a@1 b@0 c@3 d@4

Example of iteration:

map = [string_map] a@1 b@2 c@3
for p: $map
{
  k = $first($p)
  v = $second($p)
}

While the subscript is mapped to key lookup only, index-based access can be
implemented (with a bit of overhead) using the $keys() function:

map = [string_map] a@1 b@2 c@3
keys = $keys($m)
for i: $integer_sequence(0, $size($keys))
{
  k = ($keys[$i])
  v = ($map[$k])
}

Also, this commit changes the naming of other template-based value types (not
exposed as buildfile value types) to use C++ template id-like names (e.g.,
map<string,optional<bool>>).

1 files changed, 8 insertions, 2 deletions

diff --git a/tests/function/string/testscript b/tests/function/string/testscript
index 364ce42..a363cc3 100644
--- a/tests/function/string/testscript
+++ b/tests/function/string/testscript
@@ -43,8 +43,10 @@
 : size
 :
 {
-  $* <'print $size([string] abc)' >'3' : basics
-  $* <'print $size([string] )'    >'0' : zero
+  $* <'print $size([string] abc)'             >'3' : basics
+  $* <'print $size([string] )'                >'0' : zero
+  $* <'print $size([strings] a b c)'          >'3' : strings
+  $* <'print $size([string_map] a@1 b@2 c@3)' >'3' : string_map
 }
 
 : find
@@ -62,3 +64,7 @@
   $* <'print $find_index([strings] x y z, Y)'        >'3' : basics-false
   $* <'print $find_index([strings] x y z, Y, icase)' >'1' : icase
 }
+
+: keys
+:
+$* <'print $keys([string_map] a@1 b@2 c@3)' >'a b c'