map 1

package main

func main() {
	m := make(map[string]int, 3)
	x := len(m)
	m["Go"] = m["Go"]
	y := len(m)
	println(x, y)
}

Choices:

• 3 3
• 3 4
• 0 0
• 0 1

Answer: 0 1

Run it on Go play.

Key points:

• when using the make function to create a map, the second argument is neither the initial length nor the capacity of the result map. It is just a hint for Go runtime to allocate a large enough backing array to hold at least the specified number of entries.
• The length (number of entries) of the result map is zero. m["Go"] = m["Go"] is equivalent to m["Go"] = 0. After the assignment, the map contains one entry.

• slice: 1, 2, 3
• map: 1
• channel: 1
• loop: 1, 2, 3, 4
• switch: 1
• defer: 1, 2
• panic/recover: 1, 2
• reflect: 1, 2
• const: 1, 2, 3
• operator: 1, 2, 3
• function call: 1
• scope: 1, 2
• nil: 1
• embedding: 1

(more are coming ...)