refactor(go): stop emitting unused fields in go structs #2612
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Go struct fields used to be emitted for all properties of any type, including for go structs merely there to act as a proxy to a JS object. Those properties were never accessed (neither set not read), and could have been cause for confusion. They additionally needlessly increased the memory footprint of such data types. This changes the code generation to no longer emit fields on go structs that are intended as proxies to JS objects, instead embedding the base type(s) (super-class and/or super-interfaces) to properly inherit their methods without duplicating every declaration; and uses a `byte` placeholder when needed to ensure no 0-width struct is ever generated (go would have those take 0 bytes of memory, and as a consequence, any such vlaue is deemed equal to any other, which is not what we want). In cases when a member is inherited from more than one parent, that member is re-declared on the descendant type, as otherwise the promotion is ambiguous. This implied making a change to the method registration functions, such that each type (class and interface) registers a proxy `maker` function that is used by the runtime library to properly initialize jsii proxy instances of objects without requiring user intervention. This makes it safe to operate even when embedding data structures from other libraries. Additionally, it enables hiding the JS proxy structs from the exported APIs, which further reduces the risk of mis-use.
RomainMuller
added
language/go
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MrArnoldPalmer
approved these changes
Feb 26, 2021
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Go struct fields used to be emitted for all properties of any type,
including for go structs merely there to act as a proxy to a JS object.
Those properties were never accessed (neither set not read), and could
have been cause for confusion. They additionally needlessly increased
the memory footprint of such data types.
This changes the code generation to no longer emit fields on go structs
that are intended as proxies to JS objects, instead embedding the base
type(s) (super-class and/or super-interfaces) to properly inherit their
methods without duplicating every declaration; and uses a
byteplaceholder when needed to ensure no 0-width struct is ever generated
(go would have those take 0 bytes of memory, and as a consequence, any
such vlaue is deemed equal to any other, which is not what we want).
In cases when a type descends from more than one direct parent, and
any of their (transitive) bases belongs to a different assembly, all members,
including inherited, are re-implemented to avoid the risk of a conflict
occurring if two parents bring in the same declaration (then automated
promotion cannot happen anymore).
This implied making a change to the method registration functions, such
that each type (class and interface) registers a proxy
makerfunction that is used by the runtime library to properly initialize jsii
proxy instances of objects without requiring user intervention. This
makes it safe to operate even when embedding data structures from other
libraries. Additionally, it enables hiding the JS proxy structs from the
exported APIs, which further reduces the risk of mis-use.
These changes were proposed in aws/aws-cdk-rfcs#292.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.