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# v2.2.0 - yyyy-mm-dd
## Changes affecting backward compatibility
- `-d:nimStrictDelete` becomes the default. An index error is produced when the index passed to `system.delete` was out of bounds. Use `-d:nimAuditDelete` to mimic the old behavior for backwards compatibility.
- The default user-agent in `std/httpclient` has been changed to `Nim-httpclient/<version>` instead of `Nim httpclient/<version>` which was incorrect according to the HTTP spec.
- Methods now support implementations based on a VTable by using `--experimental:vtables`. Methods are then confined to be in the same module where their type has been defined.
- With `-d:nimPreviewNonVarDestructor`, non-var destructors become the default.
- A bug where tuple unpacking assignment with a longer tuple on the RHS than the LHS was allowed has been fixed, i.e. code like:
```nim
var a, b: int
(a, b) = (1, 2, 3, 4)
```
will no longer compile.
## Standard library additions and changes
[//]: # "Changes:"
- Changed `std/osfiles.copyFile` to allow to specify `bufferSize` instead of a hardcoded one.
- Changed `std/osfiles.copyFile` to use `POSIX_FADV_SEQUENTIAL` hints for kernel-level aggressive sequential read-aheads.
- `std/htmlparser` has been moved to a nimble package, use `nimble` or `atlas` to install it.
[//]: # "Additions:"
- Added `newStringUninit` to system, which creates a new string of length `len` like `newString` but with uninitialized content.
- Added `setLenUninit` to system, which doesn't initalize
slots when enlarging a sequence.
- Added `hasDefaultValue` to `std/typetraits` to check if a type has a valid default value.
- Added Viewport API for the JavaScript targets in the `dom` module.
- Added `toSinglyLinkedRing` and `toDoublyLinkedRing` to `std/lists` to convert from `openArray`s.
[//]: # "Deprecations:"
- Deprecates `system.newSeqUninitialized`, which is replaced by `newSeqUninit`.
[//]: # "Removals:"
## Language changes
- `noInit` can be used in types and fields to disable member initializers in the C++ backend.
- C++ custom constructors initializers see https://nim-lang.org/docs/manual_experimental.htm#constructor-initializer
- `member` can be used to attach a procedure to a C++ type.
- C++ `constructor` now reuses `result` instead creating `this`.
- Tuple unpacking changes:
- Tuple unpacking assignment now supports using underscores to discard values.
```nim
var a, c: int
(a, _, c) = (1, 2, 3)
```
- Tuple unpacking variable declarations now support type annotations, but
only for the entire tuple.
```nim
let (a, b): (int, int) = (1, 2)
let (a, (b, c)): (byte, (float, cstring)) = (1, (2, "abc"))
```
- An experimental option `genericsOpenSym` has been added to allow captured
symbols in generic routine bodies to be replaced by symbols injected locally
by templates/macros at instantiation time. `bind` may be used to keep the
captured symbols over the injected ones regardless of enabling the option.
Since this change may affect runtime behavior, the experimental switch
`genericsOpenSym` needs to be enabled, and a warning is given in the case
where an injected symbol would replace a captured symbol not bound by `bind`
and the experimental switch isn't enabled.
```nim
const value = "captured"
template foo(x: int, body: untyped) =
let value {.inject.} = "injected"
body
proc old[T](): string =
foo(123):
return value # warning: a new `value` has been injected, use `bind` or turn on `experimental:genericsOpenSym`
echo old[int]() # "captured"
{.experimental: "genericsOpenSym".}
proc bar[T](): string =
foo(123):
return value
assert bar[int]() == "injected" # previously it would be "captured"
proc baz[T](): string =
bind value
foo(123):
return value
assert baz[int]() == "captured"
```
## Compiler changes
- `--nimcache` using a relative path as the argument in a config file is now relative to the config file instead of the current directory.
## Tool changes
- koch now allows bootstrapping with `-d:nimHasLibFFI`, replacing the older option of building the compiler directly w/ the `libffi` nimble package in tow.
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