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A static code analysis tool with a focus on code consistency and teaching.
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lib/credo/check/warning/struct_field_amount.ex
defmodule Credo.Check.Warning.StructFieldAmount do
use Credo.Check,
id: "EX5026",
base_priority: :normal,
category: :warning,
param_defaults: [max_fields: 31],
explanations: [
check: """
Avoid structs with 32 or more fields.
Structs in Elixir are implemented as compile-time maps, which have a
predefined amount of fields.
When structs have 32 or more fields, their internal representation in
the Erlang Virtual Machines changes, potentially leading to bloating
and higher memory usage.
https://hexdocs.pm/elixir/1.19.0/code-anti-patterns.html#structs-with-32-fields-or-more
""",
params: [
max_fields: "The maximum number of field a struct should be allowed to have."
]
]
@doc false
@impl true
def run(%SourceFile{} = source_file, params) do
ctx = Context.build(source_file, params, __MODULE__)
result = Credo.Code.prewalk(source_file, &walk/2, ctx)
result.issues
end
defp walk({:defstruct, meta, [fields]} = ast, ctx) when is_list(fields) do
count = length(fields)
if count > ctx.params.max_fields do
{ast, put_issue(ctx, issue_for(ctx, meta, count))}
else
{ast, ctx}
end
end
defp walk(ast, ctx) do
{ast, ctx}
end
defp issue_for(ctx, meta, count) do
format_issue(ctx,
message: "Struct has more than #{ctx.params.max_fields} fields (#{count} found).",
trigger: "defstruct",
line_no: meta[:line],
column: meta[:column]
)
end
end