Feature #12719
closed`Struct#merge` for partial updates
Description
Other languages have operators for performing partial updates on maps. I feel like Struct could be more useful if it provided an easy way of performing partial (or full) updates.
After the change you can do the following:
Point = Struct.new(:x, :y)
p = Point.new(1, 2)
p2 = p.merge(y: 4)
p3 = p2.merge(x: 10)
p.inspect # => #<struct Point x=1, y=2>
p2.inspect # => #<struct Point x=1, y=4>
p3.inspect # => #<struct Point x=10, y=4>
p.merge!("x" => 9)
p.inspect # => #<struct Point x=9, y=2>
Files
Updated by halogenandtoast (Matthew Mongeau) about 8 years ago
- Tracker changed from Bug to Feature
Updated by halogenandtoast (Matthew Mongeau) about 8 years ago
If this is well received I think a similar syntax could be used for hashes in place of merge
.
Updated by halogenandtoast (Matthew Mongeau) about 8 years ago
- File struct_merge.patch added
As an alternative since the |
syntax might get shot down. Here's a patch adding a merge function instead:
Point = Struct.new(:x, :y)
p = Point.new(1, 2)
p2 = p.merge(y: 4)
p3 = p2.merge(x: 10)
puts p.inspect # => #<struct Point x=1, y=2>
puts p2.inspect # => #<struct Point x=1, y=4>
puts p3.inspect # => #<struct Point x=10, y=4>
Updated by nobu (Nobuyoshi Nakada) about 8 years ago
In your example, the value in the LHS is ignored when the same key is present in the RHS hash.
It doesn't feel nice as |
operator.
merge
sounds nice in that sense, but your patch would segfault at p.merge(0)
.
Updated by halogenandtoast (Matthew Mongeau) about 8 years ago
Thanks, nice catch. I'll update this tomorrow to not segfault.
Updated by halogenandtoast (Matthew Mongeau) about 8 years ago
- File struct_merge_no_segfault.patch added
Updated so it won't segfault
Updated by halogenandtoast (Matthew Mongeau) about 8 years ago
- File merge_bang.patch added
Since merge closely resembles the similar hash function, I think it makes sense to also add merge!
as a function. I'm not a fan of the mutating methods, but I would find it surprising if this interface was different. Here's an updated patch. I also fixed some of the documentation I wrote.
Updated by halogenandtoast (Matthew Mongeau) about 8 years ago
- File deleted (
struct_update.patch)
Updated by halogenandtoast (Matthew Mongeau) about 8 years ago
- File deleted (
struct_merge.patch)
Updated by halogenandtoast (Matthew Mongeau) about 8 years ago
- File deleted (
struct_merge_no_segfault.patch)
Updated by halogenandtoast (Matthew Mongeau) about 8 years ago
- File struct_merge.patch struct_merge.patch added
- Subject changed from `Struct#|` for partial updates to `Struct#merge` for partial updates
- Description updated (diff)
Update ChangeLog
Updated by halogenandtoast (Matthew Mongeau) about 8 years ago
- File deleted (
merge_bang.patch)
Updated by matz (Yukihiro Matsumoto) almost 8 years ago
- Status changed from Open to Feedback
I want to see a real-world use-case for the feature.
In addition, I don't think the name merge
is the best for the functionality.
Matz.
Updated by Eregon (Benoit Daloze) almost 8 years ago
Scala has "copy" for this purpose: some_case_class_object.copy(field: new_value)
Updated by marcotc (Marco Costa) about 3 years ago
To add a real-world use-case: in the ddtrace gem
we have a configuration Struct called AgentSettings
that holds the global defaults for our configuration:
AgentSettings = Struct.new(
:ssl,
:hostname,
:port,
:timeout_seconds,
:deprecated_for_removal_transport_configuration_proc,
:deprecated_for_removal_transport_configuration_options
) do
def initialize(
ssl:,
hostname:,
port:,
timeout_seconds:,
deprecated_for_removal_transport_configuration_proc:,
deprecated_for_removal_transport_configuration_options:,
)
super(ssl, hostname, port, timeout_seconds, deprecated_for_removal_transport_configuration_proc, \
deprecated_for_removal_transport_configuration_options)
freeze
end
end
But in a few places we want to override some of the default configuration values:
transport.adapter(
default_adapter,
agent_settings.hostname,
agent_settings.port,
# We explicitly use profiling_upload_timeout_seconds instead of agent_settings.timeout because profile
# uploads are bigger and thus we employ a separate configuration.
timeout: profiling_upload_timeout_seconds,
ssl: agent_settings.ssl
)
Today we resort to unpacking the Struct and effectively transferring the values to a hash (in the form of keyword arguments). We don't actually want our Struct to become a hash (or keyword arguments) when we pass it to #adapter
in the example above, we would like a AgentSettings
struct to be passed but with timeout
overridden.