Created
August 6, 2024 04:51
context.WithValueFunc(...)
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package context | |
import ( | |
"context" | |
"sync" | |
) | |
func WithValueFunc(ctx context.Context, key any, valFn func() any) context.Context { | |
return &valFunc{Context: ctx, key: key, valFn: valFn} | |
} | |
type valFunc struct { | |
context.Context | |
key any | |
once sync.Once | |
valFn func() any | |
val any | |
} | |
var _ context.Context = &valFunc{} | |
func (v *valFunc) Value(key any) any { | |
if key != v.key { | |
return v.Context.Value(key) | |
} | |
v.once.Do(func() { | |
v.val = v.valFn() | |
v.valFn = nil | |
}) | |
return v.val | |
} |
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