construct.go

package imbue

import (
	"context"
	"fmt"
)

// constructor is a wrapper around a function that constructs a value of type T.
//
// It implements the userFunction interface.
type constructor[T any] struct {
	// impl is the constructor implementation. It is typically a closure
	// generated by the WithX() functions. It wraps the user-provided
	// constructor function to provide a common signature.
	impl func(Context) (T, error)

	// loc is the location of the code that provided the constructor.
	loc location

	// rawErr, if true, indicates that Call() should return the error exactly as
	// it is returned by the constructor implementation, without wrapping it to
	// provide additional context.
	rawErr bool
}

// Call invokes the constructor and returns the constructed value.
func (c constructor[T]) Call(ctx context.Context, defers *deferSet) (T, error) {
	v, err := c.impl(
		&scopedContext{
			Context: ctx,
			scope:   c,
			defers:  defers,
		},
	)
	if err != nil {
		if c.rawErr {
			return v, err
		}

		return v, fmt.Errorf(
			"%s failed: %w",
			c,
			err,
		)
	}

	return v, nil
}

// Location returns the location of the code that provided the constructor.
//
// This is typically the location of the call to the WithX() function, not the
// constructor implementation function definition.
func (c constructor[T]) Location() location {
	return c.loc
}

// String returns a description of the constructor for use in error messages.
func (c constructor[T]) String() string {
	return fmt.Sprintf(
		"%s constructor (%s)",
		typeOf[T](),
		c.loc,
	)
}