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rodrigues/dialyzer_example.ex Secret

Created Dec 23, 2019
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defmodule DialyzerExamples do
# ** Dialyzer will alert if type is a superset of actual type,
# if you have `underspecs` flag on:
#
# lib/dialyzer_examples.ex:16:contract_supertype
# Type specification is a supertype of the success typing.
#
# Function:
# DialyzerExamples.foo/1
#
# Type specification:
# @spec foo(any()) :: any()
#
# Success typing:
# @spec foo(number()) :: number()
@spec foo(any()) :: any()
def foo(i), do: i + 1
def bar(i) do
case foo(i) do
n when is_number(n) ->
"yes"
_ ->
# ** Dialyzer will alert you this path can never match,
# no matter what your typespecs actually say:
#
# lib/dialyzer_examples.ex:24:pattern_match_cov
# The pattern
# :variable_
#
# can never match, because previous clauses completely cover the type
# number().
"never"
end
end
# ** Dialyzer will spot if you're missing extra types in your typespecs,
# if you have the flag `specdiffs` on:
#
# lib/dialyzer_examples.ex:38:missing_range
# The type specification is missing types returned by function.
#
# Function:
# DialyzerExamples.errorable_fun/1
#
# Type specification return types:
# ({:ok, _})
#
# Extra types in success typing:
# ({:error, :something_else})
@spec errorable_fun(term()) :: {:ok, term()}
def errorable_fun(something) do
if something do
{:ok, something}
else
{:error, :something_else}
end
end
def run(whatever) do
# ** Dialyzer will tell you if a function you call can return something
# other than `:ok` and you're not considering it,
# if you have the flag `unmatched_returns` enabled:
#
# lib/dialyzer_examples.ex:59:unmatched_return
# The expression produces a value of type:
#
# {:error, :something_else} | {:ok, _}
#
# but this value is unmatched.
errorable_fun(whatever)
:ok
end
# ** Dialyzer will tell you if you added an extra type in your typespec
# that can never be returned, by default:
#
# lib/dialyzer_examples.ex:76:extra_range
# The type specification has too many types for the function.
#
# Function:
# DialyzerExamples.baz/0
#
# Extra type:
# {:error, :nope}
#
# Success typing:
# :ok
@spec baz() :: :ok | {:error, :nope}
def baz do
:ok
end
defmodule Be do
@callback foo() :: :ok
end
defmodule Impl do
@behaviour Be
# ** Dialyzer will alert you if a callback
# is not being respected:
#
# lib/dialyzer_examples.ex:112:callback_type_mismatch
# Type mismatch for @callback foo/0 in DialyzerExamples.Be behaviour.
#
# Expected type:
# :ok
#
# Actual type:
# :nope
def foo, do: :nope
end
end
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