Patcher and interfaces for custom types to be used in expressions as standard go types #487
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patchers/value/value.go
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| // Patcher is an expr.Option that both patches the program and adds the `getExprValue` function. | ||
| // Use it directly as an Option to expr.Compile() | ||
| var Patcher = func() expr.Option { |
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Let's use patcher pkg and rename Patcher to, for example, patcher.ValueGetter.
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How should I define the actual expr.Function doing this? Should I move it somewhere else?
expr imports patcher so it creates an import cycle to create the function in patcher.
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Any advice on where I should define the expr.Function without causing an import cycle?
I don't think it should be defined as a normal builtin function?
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Sorry, I didn't understand the question.
I mean this: lets move code to patchers dir and rename this function to ValueGetter.
patchers/value/value.go
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| // Use it directly as an Option to expr.Compile() | ||
| var Patcher = func() expr.Option { | ||
| vPatcher := patcher{} | ||
| return func(c *conf.Config) { |
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We can reuse expr.Patch helper here.
patchers/value/value.go
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| func getExprValue(params ...any) (any, error) { | ||
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| switch v := params[0].(type) { | ||
| case ExprValuer: |
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What about creating a separate function for each type?
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Would this be for performance reasons? I didn't want to pollute the expr function space with a bunch of functions.
I want to preserve the ability to implement both Any and a specific type interface. This lets you get compile type checks for the type, but still return nil at runtime. So, even if specific functions for each type were implemented, a type check would still need to be done. In some quick testing I had done earlier it seemed like as soon as you were paying the cost of type checking it didn't really matter the number of branches in the switch, or if you broke it into an if statement.
I can revisit if you would like.
patchers/value/value.go
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| // Package value provides a Patcher that uses interfaces to allow custom types that can be represented as standard go values to be used more easily in expressions. | |||
| // | |||
| // # Example Usage | |||
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Let's add documentation about motivation and there this patcher can be used.
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Please see 6be8f0e
Let me know if you would like anything additional.
See #460 for previous discussion.
I tried to cover all the types supported by expr, as well generic
map[string]anyand[]any.To take advantage of the interfaces you use
value.Patcheras an option when compiling an expression.