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43 lines
855 B
Markdown
43 lines
855 B
Markdown
# Append To A Keyword List
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If you have two keyword lists, you can append them like so:
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```elixir
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> a = [a: 1]
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[a: 1]
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> b = [b: 2]
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[b: 2]
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> a ++ b
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[a: 1, b: 2]
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```
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But what if something a bit more programmatic is happening and you are
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building up the additions to the keyword list based on variables?
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```elixir
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> x = :x
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:x
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> c = a ++ [x 5]
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** (CompileError) iex:5: undefined function x/1
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(stdlib) lists.erl:1353: :lists.mapfoldl/3
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(stdlib) lists.erl:1354: :lists.mapfoldl/3
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```
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That makes elixir think `x` is some function when in fact it is just a
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variable containing the keyword `:x`.
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Simply adding a comma doesn't quite do it either.
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```elixir
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> c = a ++ [x, 5]
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[{:a, 1}, :x, 5]
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```
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We need to wrap the internal part with curly braces to create the tuple that
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can then be appended to `a`.
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```elixir
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> c = a ++ [{x, 5}]
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[a: 1, x: 5]
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```
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