builtin: make array.delete() reallocate, provide .delete_many() (#10889)

doc/docs.md

@@ -862,6 +862,9 @@ There are further built in methods for arrays:
 * `a.prepend(arr)` insert elements of array `arr` at beginning
 * `a.trim(new_len)` truncate the length (if `new_length < a.len`, otherwise do nothing)
 * `a.clear()` empty the array (without changing `cap`, equivalent to `a.trim(0)`)
+* `a.delete_many(start, size)` removes `size` consecutive elements beginning with index `start`
+  &ndash; triggers reallocation
+* `a.delete(index)` equivalent to `a.delete_many(index, 1)`
 * `v := a.first()` equivalent to `v := a[0]`
 * `v := a.last()` equivalent to `v := a[a.len - 1]`
 * `v := a.pop()` get last element and remove it from array

vlib/builtin/array.v

@@ -200,15 +200,30 @@ pub fn (mut a array) prepend_many(val voidptr, size int) {
 
 // delete deletes array element at index `i`.
 pub fn (mut a array) delete(i int) {
+	a.delete_many(i, 1)
+}
+
+// delete_many deletes `size` elements beginning with index `i`
+pub fn (mut a array) delete_many(i int, size int) {
 	$if !no_bounds_checking ? {
-		if i < 0 || i >= a.len {
-			panic('array.delete: index out of range (i == $i, a.len == $a.len)')
+		if i < 0 || i + size > a.len {
+			endidx := if size > 1 { '..${i + size}' } else { '' }
+			panic('array.delete: index out of range (i == $i$endidx, a.len == $a.len)')
 		}
 	}
 	// NB: if a is [12,34], a.len = 2, a.delete(0)
 	// should move (2-0-1) elements = 1 element (the 34) forward
-	unsafe { C.memmove(a.get_unsafe(i), a.get_unsafe(i + 1), (a.len - i - 1) * a.element_size) }
-	a.len--
+	old_data := a.data
+	new_size := a.len - size
+	new_cap := if new_size == 0 { 1 } else { new_size }
+	a.data = vcalloc(new_cap * a.element_size)
+	unsafe { C.memcpy(a.data, old_data, i * a.element_size) }
+	unsafe {
+		C.memcpy(&byte(a.data) + i * a.element_size, &byte(old_data) + (i + size) * a.element_size,
+			(a.len - i - size) * a.element_size)
+	}
+	a.len = new_size
+	a.cap = new_cap
 }
 
 // clear clears the array without deallocating the allocated data.

vlib/builtin/array_test.v

@@ -65,6 +65,34 @@ fn test_deleting() {
 	assert a.len == 2
 }
 
+fn test_slice_delete() {
+	mut a := [1.5, 2.5, 3.25, 4.5, 5.75]
+	b := a[2..4]
+	a.delete(0)
+	assert a == [2.5, 3.25, 4.5, 5.75]
+	assert b == [3.25, 4.5]
+	a = [3.75, 4.25, -1.5, 2.25, 6.0]
+	c := a[..3]
+	a.delete(2)
+	assert a == [3.75, 4.25, 2.25, 6.0]
+	assert c == [3.75, 4.25, -1.5]
+}
+
+fn test_delete_many() {
+	mut a := [1, 2, 3, 4, 5, 6, 7, 8, 9]
+	b := a[2..6]
+	a.delete_many(4, 3)
+	assert a == [1, 2, 3, 4, 8, 9]
+	assert b == [3, 4, 5, 6]
+	c := a[..a.len]
+	a.delete_many(2, 0) // this should just clone
+	a[1] = 17
+	assert a == [1, 17, 3, 4, 8, 9]
+	assert c == [1, 2, 3, 4, 8, 9]
+	a.delete_many(0, a.len)
+	assert a == []int{}
+}
+
 fn test_short() {
 	a := [1, 2, 3]
 	assert a.len == 3