60 lines
1.2 KiB
Go
60 lines
1.2 KiB
Go
// For more tutorials: https://blog.learngoprogramming.com
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//
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// Copyright © 2018 Inanc Gumus
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// Learn Go Programming Course
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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//
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package main
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import (
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"fmt"
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"strings"
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)
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type item interface {
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discount(ratio float64)
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// ~~ interface embedding ~~
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//
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// item interface embeds the fmt.Stringer interface.
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//
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// Go adds the methods of the fmt.Stringer
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// to this item interface.
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//
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// same as this:
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// String() string
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fmt.Stringer
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}
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type list []item
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// String method makes the list an fmt.Stringer.
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func (l list) String() string {
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if len(l) == 0 {
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return "Sorry. We're waiting for delivery 🚚."
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}
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// use the strings.Builder when you're combining
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// a long list of strings together.
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var str strings.Builder
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for _, it := range l {
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// the builder.WriteString doesn't know about the stringer interface.
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// because it takes a string argument.
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// so, you need to call the String method yourself.
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str.WriteString(it.String())
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str.WriteRune('\n')
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// or slower way:
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// fmt.Fprintln(&str, it)
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}
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return str.String()
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}
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func (l list) discount(ratio float64) {
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for _, it := range l {
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it.discount(ratio)
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}
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}
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