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---
stage: none
group: unassigned
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
---
# GitLab utilities
We have developed a number of utilities to help ease development:
## `MergeHash`
Refer to: <https://gitlab.com/gitlab-org/gitlab/blob/master/lib/gitlab/utils/merge_hash.rb>:
- Deep merges an array of hashes:
``` ruby
Gitlab::Utils::MergeHash.merge(
[{ hello: ["world"] },
{ hello: "Everyone" },
{ hello: { greetings: ['Bonjour', 'Hello', 'Hallo', 'Dzien dobry'] } },
"Goodbye", "Hallo"]
)
```
Gives:
``` ruby
[
{
hello:
[
"world",
"Everyone",
{ greetings: ['Bonjour', 'Hello', 'Hallo', 'Dzien dobry'] }
]
},
"Goodbye"
]
```
- Extracts all keys and values from a hash into an array:
``` ruby
Gitlab::Utils::MergeHash.crush(
{ hello: "world", this: { crushes: ["an entire", "hash"] } }
)
```
Gives:
``` ruby
[:hello, "world", :this, :crushes, "an entire", "hash"]
```
## `Override`
Refer to [`override.rb`](https://gitlab.com/gitlab-org/gitlab/blob/master/lib/gitlab/utils/override.rb):
- This utility can help you check if one method would override
another or not. It is the same concept as Java's `@Override` annotation
or Scala's `override` keyword. However, we only run this check when
`ENV['STATIC_VERIFICATION']` is set to avoid production runtime overhead.
This is useful for checking:
- If you have typos in overriding methods.
- If you renamed the overridden methods, which make the original override methods
irrelevant.
Here's a simple example:
``` ruby
class Base
def execute
end
end
class Derived < Base
extend ::Gitlab::Utils::Override
override :execute # Override check happens here
def execute
end
end
```
This also works on modules:
``` ruby
module Extension
extend ::Gitlab::Utils::Override
override :execute # Modules do not check this immediately
def execute
end
end
class Derived < Base
prepend Extension # Override check happens here, not in the module
end
```
Note that the check will only happen when either:
- The overriding method is defined in a class, or:
- The overriding method is defined in a module, and it's prepended to
a class or a module.
Because only a class or prepended module can actually override a method.
Including or extending a module into another cannot override anything.
## `StrongMemoize`
Refer to <https://gitlab.com/gitlab-org/gitlab/blob/master/lib/gitlab/utils/strong_memoize.rb>:
- Memoize the value even if it is `nil` or `false`.
We often do `@value ||= compute`. However, this doesn't work well if
`compute` might eventually give `nil` and you don't want to compute again.
Instead you could use `defined?` to check if the value is set or not.
It's tedious to write such pattern, and `StrongMemoize` would
help you use such pattern.
Instead of writing patterns like this:
``` ruby
class Find
def result
return @result if defined?(@result)
@result = search
end
end
```
You could write it like:
``` ruby
class Find
include Gitlab::Utils::StrongMemoize
def result
strong_memoize(:result) do
search
end
end
end
```
- Clear memoization
``` ruby
class Find
include Gitlab::Utils::StrongMemoize
end
Find.new.clear_memoization(:result)
```
## `RequestCache`
Refer to [`request_cache.rb`](https://gitlab.com/gitlab-org/gitlab/blob/master/lib/gitlab/cache/request_cache.rb).
This module provides a simple way to cache values in RequestStore,
and the cache key would be based on the class name, method name,
optionally customized instance level values, optionally customized
method level values, and optional method arguments.
A simple example that only uses the instance level customised values is:
``` ruby
class UserAccess
extend Gitlab::Cache::RequestCache
request_cache_key do
[user&.id, project&.id]
end
request_cache def can_push_to_branch?(ref)
# ...
end
end
```
This way, the result of `can_push_to_branch?` would be cached in
`RequestStore.store` based on the cache key. If `RequestStore` is not
currently active, then it would be stored in a hash, and saved in an
instance variable so the cache logic would be the same.
We can also set different strategies for different methods:
``` ruby
class Commit
extend Gitlab::Cache::RequestCache
def author
User.find_by_any_email(author_email)
end
request_cache(:author) { author_email }
end
```
## `ReactiveCaching`
Read the documentation on [`ReactiveCaching`](reactive_caching.md).
|
