45 lines
1.1 KiB
Go
45 lines
1.1 KiB
Go
package opt
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// Then applies the function ‘fn’ to the value inside of the optional-type ‘op’, if the optional-type ‘op’ is holding something, and returns the resulting optional-type.
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// If the optional-type ‘op’ is holding nothing, then Then also returns nothing.
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//
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// For example:
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//
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// fn := func(s string) opt.Optional[byte] {
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//
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// if len(s) < 2 {
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// return opt.Nothing[byte]()
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// }
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//
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// return opt.Something[byte](s[1])
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// }
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//
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// var op opt.Optional[string] = opt.Something("Hello world!"")
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//
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// var result opt.Optional[byte] = opt.Then(op, fn)
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//
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// // result == opt.Something[byte]('e')
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//
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// // ...
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//
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// var op2 opt.Optional[string] = opt.Something[string]("X")
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//
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// var result2 opt.Optional[byte] = opt.Then(op, fn)
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//
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// // result2 == opt.Nothing[byte]()
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//
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// // ...
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//
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// var op2 opt.Optional[string] = opt.Nothing[string]()
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//
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// var result2 opt.Optional[byte] = opt.Then(op, fn)
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//
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// // result2 == opt.Nothing[byte]()
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func Then[T1 any, T2 any](op Optional[T1], fn func(T1)Optional[T2]) Optional[T2] {
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if op.isnothing() {
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return Nothing[T2]()
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}
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return fn(op.value)
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}
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