proposal: Go 2: struct tag interpolation of constants #66108
Comments
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Related proposal for structured tags #23637 |
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This proposal is not backward compatible. It would change the meaning of existing struct tags that contain a |
While the example syntax I provided may not be backwards compatible, I don’t think it should be very hard to figure out a backwards compatible syntax. For example, prefixing the entire struct tag with a dollar sign could be what sets it apart for the compiler, and then brackets can be used to interpolate the actual constant, like so: const ColName = “name”
type User struct {
Name string $`db:”{ColName}”`
}I believe that syntax would be 100% backwards compatible |
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We've discussed a lot of these issues at #34174 and friends. |
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No change in consensus. |
Go Programming Experience
Intermediate
Other Languages Experience
Python, JS, C#, Java
Related Idea
Has this idea, or one like it, been proposed before?
It feels like it must've before, but I couldn't find anything like it.
Does this affect error handling?
No.
Is this about generics?
No.
Proposal
Go supports adding tags to struct fields. This feature has been frequently used in packages used for ORMs, unmarshalling, code generation, struct validation, and more. It is not uncommon to see multiple values provided under a given tag, such as the
jsontag, orvalidatetag. These values are often separated by a literal comma, and an equals sign is generally used more or less as an assignment operator. A common convention is also to have the first value associated with a given tag define the name of the field within the context of that tag. Here is a somewhat overloaded example of such tags:In the case of interacting with a database, I have also found myself on occasion declaring a constant with the name of the db column, for example:
const ColAge = "age"Another semi-common pattern I have found is the use of a characters hex value to avoid issues with parsing struct tag values. For example:
Commonly used struct tag parsing packages end up extracting the
Fielddoc tag into three parts, due to the comma within the description. The offered solution is typically something along the lines of using the hex representation of a comma0x2C, which would look like this:I propose adding language support for interpolating constants into struct fields, which would hopefully improve readability, and reduce repetition. I don't have a desired exact syntax in mind, beyond of course that it would need to be backwards compatible. With the addition of this feature, the above examples could look something like this:
Language Spec Changes
No response
Informal Change
This change would allow interpolating constants in struct tags. Something like this:
Is this change backward compatible?
I believe it could be with careful consideration.
Orthogonality: How does this change interact or overlap with existing features?
The improvement would be in code readability.
Would this change make Go easier or harder to learn, and why?
It would be harder due to having another feature to learn, but the learning curve is minute.
Cost Description
A change to the compiler to handle the additional syntax. I am not super familiar with the compiler's implementation, but I expect it would be easy.
Changes to Go ToolChain
go
Performance Costs
the compile time cost would exist, but should be small
Prototype
No response
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