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Author SHA1 Message Date
nick-w-nick
179ec70c2f Merge 295fe153ad into 5e19d53382 2024-12-29 23:15:32 -05:00
jbranchaud
5e19d53382 Add Pass A Struct To A Function as a Go TIL 2024-12-29 10:26:55 -07:00
nick-w-nick
295fe153ad added mention of ES6 compatibility
Hello, I've added a small blockquote below the description to indicate that this method of accessing an indefinite number of function arguments has been superseded by the use of the spread operator via rest parameters for ES6+ compatibility.
2022-01-06 11:39:04 -05:00
3 changed files with 69 additions and 1 deletions

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@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
_1551 TILs and counting..._
_1552 TILs and counting..._
---
@@ -415,6 +415,7 @@ _1551 TILs and counting..._
- [Not So Random](go/not-so-random.md)
- [Parse A String Into Individual Fields](go/parse-a-string-into-individual-fields.md)
- [Parse Flags From CLI Arguments](go/parse-flags-from-cli-arguments.md)
- [Pass A Struct To A Function](go/pass-a-struct-to-a-function.md)
- [Produce The Zero Value Of A Generic Type](go/produce-the-zero-value-of-a-generic-type.md)
- [Redirect File To Stdin During Delve Debug](go/redirect-file-to-stdin-during-delve-debug.md)
- [Replace The Current Process With An External Command](go/replace-the-current-process-with-an-external-command.md)

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@@ -0,0 +1,65 @@
# Pass A Struct To A Function
Go operates as _pass-by-value_ which means that when we pass a struct to a
function, the receiving function gets a copy of the struct. Two things worth
noticing about that are 1) an extra memory allocation happens when calling the
function and 2) altering the struct does not affect the original in the calling
context.
On the other hand, we can have a function that takes a pointer to a struct.
When we call that function, we have a reference to the memory location of the
struct instead of a copy of the struct. That means no additional allocation and
modifications to the dereferenced struct are modifications to the original in
the calling context.
Here is an example that demonstrates both of these. Notice the printed output
that is included in comments at the end which shows memory locations and
contents of the struct at various points.
```go
package main
import "fmt"
type Order struct {
Item string
Quantity int
DineIn bool
}
func main() {
order := Order{Item: "taco", Quantity: 3, DineIn: true}
fmt.Println("Order:", order)
fmt.Printf("main - Loc: %p\n", &order)
doubledOrder := doubleOrder(order)
fmt.Println("Double Order:", doubledOrder)
fmt.Println("Original Order:", order)
doubleOrderPtr(&order)
fmt.Println("Double Order Ptr:", order)
}
func doubleOrder(order Order) Order {
fmt.Printf("doubleOrder - Loc: %p\n", &order)
order.Quantity *= 2
return order
}
func doubleOrderPtr(order *Order) {
fmt.Printf("doubleOrderPtr - Loc: %p\n", order)
(*order).Quantity *= 2
}
// Order: {taco 3 true}
// main - Loc: 0xc0000b4000
// doubleOrder - Loc: 0xc0000b4040
// Double Order: {taco 6 true}
// Original Order: {taco 3 true}
// doubleOrderPtr - Loc: 0xc0000b4000
// Double Order Ptr: {taco 6 true}
```

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@@ -5,6 +5,8 @@ an array-like object with all of the arguments to the function. Even if not
all of the arguments are referenced in the function signature, they can
still be accessed via the `arguments` object.
> For ES6+ compatibility, the `spread` operator used via [rest parameters](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters) is preferred over the `arugments` object when accessing an abritrary number of function arguments.
```javascript
function argTest(one) {
console.log(one);