denna
Something like a Map with patterns as keys
I am brainstorming how to create a data-structure that contains anonymous functions that are used if a value matches a pattern. The data-structure needs to change dynamically.
A map seems to fit:
%{{1,2,3} => :func_a,{2,3,4} => :func_b}[{1,2,3}]
But the key is not a pattern it would be great to be able to do so.
I was hoping that it could be specified like a case statement:
case {1, 2, 3} do
{4, 5, 6} ->
"This clause won't match"
{1, 2, x} ->
"This clause will match and bind x to 3 in this clause"
_ ->
"This clause would match any value"
end
like this:
%{{1,2,_} => :func_a,{2,3,_} => :func_b}[{1,2,3}]
but this is not possible.
any suggestions?
Most Liked
dimitarvp
Not sure I get what you want but storing patterns like {1, 2, x} is not possible in Elixir.
Can you demonstrate one complete case of what would a successful implementation achieve and do?
josevalim
Maps are hash tables (for 32+ elements) indexed by key. Therefore a lookup such as {1, 2, _}, where we don’t fully have to key to hash, would require a linear traversal of all keys. In other words, maps are really not a good fit for the lookups you want to perform, regardless of Elixir having syntax for it or not.
Luckily, a relatively straight-forward solution is to nest your keys:
map = %{{1,2} => %{3 => :func_a},{2,3} => %{4 => :func_b}}
This way, if you want to lookup 1, 2, 3, you do:
map[{1, 2}][3]
if you want any (or all) keys starting with {1, 2}, then you do:
map[{1, 2}]
wolf4earth
Something which might be interesting for you could be :ets.fun2ms which transforms a function to an ets match specification.
hauleth
Well, partially you can by using match spec and then using :erlang.match_spec_test([value], match_spec, :table).
Popular in Questions
Other popular topics
Latest on Elixir Forum
Sponsor Spotlight
Enabling companies to succeed by building software people love.
Categories:
Sub Categories:
Forums
Our Sponsors
Build Elixir applications with speed and confidence.
Supporting innovation across the BEAM ecosystem.
We build reliable cloud platforms for business-critical systems.
Catch errors, track performance, monitor hosts and more.
Develop your skills with books, videos, and courses.
Producing high quality Elixir screencasts since 2017.
Enabling companies to succeed by building software people love.
Courses that'll move you from confusion to "Aha, now I get it!"