v/vlib/strings/builder.v

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V

// Copyright (c) 2019-2021 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module strings
// strings.Builder is used to efficiently append many strings to a large
// dynamically growing buffer, then use the resulting large string. Using
// a string builder is much better for performance/memory usage than doing
// constantly string concatenation.
pub struct Builder {
pub mut:
buf []byte
str_calls int
len int
initial_size int = 1
}
// new_builder returns a new string builder, with an initial capacity of `initial_size`
pub fn new_builder(initial_size int) Builder {
return Builder{
// buf: make(0, initial_size)
buf: []byte{cap: initial_size}
str_calls: 0
len: 0
initial_size: initial_size
}
}
// write_bytes appends `bytes` to the accumulated buffer
pub fn (mut b Builder) write_bytes(bytes byteptr, howmany int) {
b.buf.push_many(bytes, howmany)
b.len += howmany
}
// write_b appends a single `data` byte to the accumulated buffer
pub fn (mut b Builder) write_b(data byte) {
b.buf << data
b.len++
}
// write appends the string `s` to the buffer
[inline]
pub fn (mut b Builder) write(s string) {
if s == '' {
return
}
b.buf.push_many(s.str, s.len)
// for c in s {
// b.buf << c
// }
// b.buf << []byte(s) // TODO
b.len += s.len
}
// go_back discards the last `n` bytes from the buffer
pub fn (mut b Builder) go_back(n int) {
b.buf.trim(b.buf.len - n)
b.len -= n
}
fn bytes2string(b []byte) string {
mut copy := b.clone()
copy << byte(`\0`)
res := tos(copy.data, copy.len - 1)
return res
}
// cut_last cuts the last `n` bytes from the buffer and returns them
pub fn (mut b Builder) cut_last(n int) string {
res := bytes2string(b.buf[b.len - n..])
b.buf.trim(b.buf.len - n)
b.len -= n
return res
}
/*
pub fn (mut b Builder) cut_to(pos int) string {
res := bytes2string( b.buf[pos..] )
b.buf.trim(pos)
b.len = pos
return res
}
*/
// go_back_to resets the buffer to the given position `pos`
// NB: pos should be < than the existing buffer length.
pub fn (mut b Builder) go_back_to(pos int) {
b.buf.trim(pos)
b.len = pos
}
// writeln appends the string `s`, and then a newline character.
[inline]
pub fn (mut b Builder) writeln(s string) {
// for c in s {
// b.buf << c
// }
b.buf.push_many(s.str, s.len)
// b.buf << []byte(s) // TODO
b.buf << `\n`
b.len += s.len + 1
}
// buf == 'hello world'
// last_n(5) returns 'world'
pub fn (b &Builder) last_n(n int) string {
if n > b.len {
return ''
}
return bytes2string(b.buf[b.len - n..])
}
// buf == 'hello world'
// after(6) returns 'world'
pub fn (b &Builder) after(n int) string {
if n >= b.len {
return ''
}
return bytes2string(b.buf[n..])
}
// str returns all of the accumulated content of the buffer.
// NB: in order to avoid memleaks and additional memory copies, after a call to b.str(),
// the builder b will be empty. The returned string *owns* the accumulated data so far.
pub fn (mut b Builder) str() string {
b.str_calls++
if b.str_calls > 1 {
panic('builder.str() should be called just once.\nIf you want to reuse a builder, call b.free() first.')
}
b.buf << `\0`
s := tos(b.buf.data, b.len)
bis := b.initial_size
// free(b.buf.data)
b.buf = []byte{cap: bis}
b.len = 0
return s
}
// manually free the contents of the buffer
pub fn (mut b Builder) free() {
unsafe { free(b.buf.data) }
// b.buf = []byte{cap: b.initial_size}
b.len = 0
b.str_calls = 0
}