Improved support for read-only arrays and tuples by ahejlsberg · Pull Request #29435 · microsoft/TypeScript · GitHub

This PR improves our support for read-only arrays and tuples:

readonly modifier on array types: readonly T[] corresponds to ReadonlyArray<T> (similar to how T[] corresponds to Array<T>).
readonly modifier on tuple types: readonly [T0, T1, ...] correponds to a tuple type that derives from ReadonlyArray<T0 | T1 | ...> and has read-only element positions.
Support for read-only arrays and tuples in mapped types. When a mapped type specifies a +readonly modifier, read-write array and tuple types are mapped to their read-only form, and when a mapped type specifies a -readonly modifier, read-only array types and tuples are mapped to their read-write form. This means that Readonly<T> now produces read-only forms of arrays and tuples.

Some examples:

function f1(mt: [number, number], rt: readonly [number, number]) {
    mt[0] = 1;  // Ok
    rt[0] = 1;  // Error, read-only element
}

function f2(ma: string[], ra: readonly string[], mt: [string, string], rt: readonly [string, string]) {
    ma = ra;  // Error
    ma = mt;  // Ok
    ma = rt;  // Error
    ra = ma;  // Ok
    ra = mt;  // Ok
    ra = rt;  // Ok
    mt = ma;  // Error
    mt = ra;  // Error
    mt = rt;  // Error
    rt = ma;  // Error
    rt = ra;  // Error
    rt = mt;  // Ok
}

type ReadWrite<T> = { -readonly [P in keyof T] : T[P] };

type T0 = Readonly<string[]>;  // readonly string[]
type T1 = Readonly<[number, number]>;  // readonly [number, number]
type T2 = Partial<Readonly<string[]>>;  // readonly (string | undefined)[]
type T3 = Readonly<Partial<string[]>>;  // readonly (string | undefined)[]
type T4 = ReadWrite<Required<T3>>;  // string[]

Fixes #26864.
Fixes #28540.
Fixes #28968.

Typo: typle to tuple.

Jordi Oliveras Rovira (@j-oliveras) Oops. Thanks!

Add test for this?

Think we need test/handling for .d.ts generation and decorator for this new typeNode kind.

Does this improved support for readonly arrays mean it's now possible to have readonly array/tuples as the type of a rest argument?

function f(...args: ReadonlyArray<string>) {} is currently a type error.

@Kovensky Isn't in the PR currently, but I see no reason why we couldn't support it. I will fix it, it's just a minor change.

+1 for .d.ts emit coverage - the only .d.ts currently in this set has semantic errors in its originating file, which makes it shaky at best

I think having decorator test is good idea too.. since we normally forget that when we enable new kind of type annotation.

// @emitDecoratorMetadata: true
// @experimentalDecorators: true
// @declaration: true

declare const someDec: any;
class A {
  @someDec
  j: readonly string[];
  @someDec
  k: readonly [string, number];
}

Is this an intended change that a single 'readonly' is no longer parsed as a type?
Such code compiled fine before this change:

type readonly = string;
var q: readonly;

(This is not a sample from real code, just a test case.)

Seems that it is not a serious issue, but would be nice to know if this was planned, as you still may declare a type named 'readonly' but cannot use it anymore.

Anton Lobov (@zhuravlikjb) No, that was not intended. I will look at getting it fixed.

Using a version of TypeScript that contains this PR creates declaration files which are not compatible with older versions of TypeScript.

In case someone else has the same problem: I created a transformer to downlevel readonly array types in declaration files: https://github.com/ajafff/ts-transform-readonly-array

Anders Hejlsberg (@ahejlsberg) This feature leaved some large bugs (Maybe regression). Please fix them: #29442 #29702

falsandtru (@falsandtru) Those issues are not related to this PR, but I have a fix in #29740.

Indeed, I thought another PR. Anyway, thanks for fixing.

I assume the extension to readonly SomeObject or readonly T is not worth the native compiler support, now that Readonly<T> can work for everything as expected? React.Ref<readonly T> such that it's assignable from Ref<U> for U extends T would be kind of neat though.

Is it still possible to declare a writable property with an immutable array? For example, constructable stylesheets defines document.adoptedStyleSheets as an array that is immutable and needs to be reassigned to be changed:

element.shadowRoot.adoptedStyleSheets = [...element.shadowRoot.adoptedStyleSheets, styleSheet]

Anders Hejlsberg (ahejlsberg) added 6 commits January 12, 2019 08:45

Respect readonly mapped type modifier when mapping arrays and tuples

903863a

Support 'readonly' type modifier on array and tuple types

bb8378f

Accept new baselines

7b00a29

Update array/tuple relationship checking

db840f4

Add tests

cff7874

Accept new baselines

a7ca7f4

Anders Hejlsberg (ahejlsberg) requested review from Daniel Rosenwasser (DanielRosenwasser) and Ryan Cavanaugh (RyanCavanaugh) January 15, 2019 23:42

Jordi Oliveras Rovira (j-oliveras) reviewed Jan 16, 2019

View reviewed changes

Igor Oleinikov (Igorbek) mentioned this pull request Jan 16, 2019

Covariance / Contravariance Annotations #1394

Closed

Sheetal Nandi (sheetalkamat) reviewed Jan 16, 2019

View reviewed changes

Anders Hejlsberg (ahejlsberg) added 3 commits January 16, 2019 09:46

Fix typo

2256f91

Add more tests

2ccc106

Accept new baselines

b611a51

Sheetal Nandi (sheetalkamat) reviewed Jan 16, 2019

View reviewed changes

Anders Hejlsberg (ahejlsberg) added 2 commits January 16, 2019 12:45

Add .d.ts generation test

0eac506

Accept new baselines

d24a63d

Claudia Meadows (dead-claudia) mentioned this pull request Jan 16, 2019

Add a mutating return type operator to indicate whether a function modifies a property indirectly #29346

Closed

5 tasks

Anders Hejlsberg (ahejlsberg) added 3 commits January 17, 2019 06:06

Allow rest parameter type to be a readonly array or tuple

e581649

Add tests

2200d35

Accept new baselines

ef89d26

Sheetal Nandi (sheetalkamat) added a commit to microsoft/TypeScript-TmLanguage that referenced this pull request Jan 18, 2019

Readonly modifier support from PR microsoft/TypeScript#29435

76cfeab

Anders Hejlsberg (ahejlsberg) mentioned this pull request Jan 21, 2019

Const contexts for literal expressions #29510

Merged

Daniel Rosenwasser (DanielRosenwasser) mentioned this pull request Jan 24, 2019

Design Meeting Notes, 1/18/2019 #29568

Closed

Ryan Cavanaugh (RyanCavanaugh) requested changes Jan 25, 2019

View reviewed changes

Ryan Cavanaugh (RyanCavanaugh) assigned Anders Hejlsberg (ahejlsberg) Jan 25, 2019

Anders Hejlsberg (ahejlsberg) deleted the readonlyArrayTuple branch January 30, 2019 23:59

Gerhard Stöbich (Flarna) mentioned this pull request Jan 31, 2019

[node] correct SlowBuffer DefinitelyTyped/DefinitelyTyped#32661

Merged

9 tasks

Mohsen Azimi (mohsen1) mentioned this pull request Feb 5, 2019

readonly function arguments #29742

Closed

5 tasks

This was referenced Feb 13, 2019

TypeScript 3.4 meta-issue babel/babel#9502

Closed

TypeScript readonly type modifier babel/babel#9503

Closed

ikokostya mentioned this pull request Feb 14, 2019

ReadonlyArray with rest parameters #15972

Closed

ulrichb mentioned this pull request Feb 24, 2019

Generic argument type inference regression in TS 3.4 #30074

Closed

Titian Cernicova-Dragomir (dragomirtitian) mentioned this pull request Mar 8, 2019

DeepReadonly type fails to compile on typescript 3.1.1+ #29566

Closed

Daniel Rosenwasser (DanielRosenwasser) mentioned this pull request Mar 8, 2019

TypeScript 3.4 Iteration Plan #30281

Closed

Jeffrey Berry (jberry93) mentioned this pull request Mar 10, 2019

TypeScript Computed Properties jberry93/jeffreyberry.dev#4

Open

Ben Chambers (bjchambers) mentioned this pull request Mar 28, 2019

readonly mapped type modifiers for Map / ReadonlyMap #30633

Open

5 tasks

Klaus Meinhardt (ajafff) mentioned this pull request Mar 30, 2019

3.4.1 breaks backward compatibility for users of ReadonlyArray #30662

Closed

Piotr Monwid-Olechnowicz (hasparus) mentioned this pull request Apr 1, 2019

Upgrade to TypeScript version 3.4 codesandbox/codesandbox-client#1683

Closed

PopGoesTheWza (PopGoesTheWza) mentioned this pull request Apr 3, 2019

TypeError: Cannot read property 'instantiations' of undefined when use as const #30664

Closed

Igor Bezkrovnyi (ibezkrovnyi) mentioned this pull request Apr 12, 2019

[@types/prop-types] Add support of as const to oneOf DefinitelyTyped/DefinitelyTyped#34706

Merged

Anders Hejlsberg (ahejlsberg) mentioned this pull request Jun 7, 2019

Regression in array destruction in TypeScript 3.3 #29731

Closed

Ben Grynhaus (bengry) mentioned this pull request Jun 11, 2019

Take a readonly array when possible mobxjs/mobx-state-tree#1314

Closed

3 tasks

Joe Calzaretta (jcalz) mentioned this pull request Jul 15, 2019

Playground: code formmating broken with TS3.4+ readonly notation microsoft/TypeScript-Website#32

Closed

Natan Sągol (merlinnot) mentioned this pull request Jul 24, 2019

error TS1005: ';' expected on tsc firebase/firebase-functions#404

Closed

Jack Williams (jack-williams) mentioned this pull request Aug 13, 2019

Support readonly types with inference #32812

Closed

5 tasks

Nathan Shively-Sanders (sandersn) mentioned this pull request Feb 3, 2020

Do not materialize optional undefined properties inside actual types #28727

Closed

Microsoft (microsoft) locked as resolved and limited conversation to collaborators Oct 16, 2025

                       "category": "Error",
                       "code": 1353
                   },
+                  "'readonly' type modifier is only permitted on array and typle types.": {

                           switch (operator) {
                               case SyntaxKind.KeyOfKeyword:
                               case SyntaxKind.UniqueKeyword:
+                              case SyntaxKind.ReadonlyKeyword:

                           }
+                          else if (node.operator === SyntaxKind.ReadonlyKeyword) {
+                              if (node.type.kind !== SyntaxKind.ArrayType && node.type.kind !== SyntaxKind.TupleType) {
+                                  return grammarErrorOnFirstToken(node, Diagnostics.readonly_type_modifier_is_only_permitted_on_array_and_typle_types, tokenToString(SyntaxKind.SymbolKeyword));

Improved support for read-only arrays and tuples by ahejlsberg · Pull Request #29435 · microsoft/TypeScript · GitHub

Uh oh!

Improved support for read-only arrays and tuples - #29435

Improved support for read-only arrays and tuples#29435Anders Hejlsberg (ahejlsberg) merged 27 commits intomastermicrosoft/TypeScript:masterfrom readonlyArrayTuplemicrosoft/TypeScript:readonlyArrayTupleCopy head branch name to clipboard

Conversation

Anders Hejlsberg (ahejlsberg) commented Jan 15, 2019 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Jordi Oliveras Rovira (j-oliveras) Jan 16, 2019

Choose a reason for hiding this comment

Uh oh!

Anders Hejlsberg (ahejlsberg) Jan 16, 2019

Choose a reason for hiding this comment

Uh oh!

Sheetal Nandi (sheetalkamat) Jan 16, 2019

Choose a reason for hiding this comment

Uh oh!

Sheetal Nandi (sheetalkamat) Jan 16, 2019

Choose a reason for hiding this comment

Uh oh!

Jessica Franco (Jessidhia) commented Jan 17, 2019

Uh oh!

Anders Hejlsberg (ahejlsberg) commented Jan 17, 2019

Uh oh!

Ryan Cavanaugh (RyanCavanaugh) left a comment

Choose a reason for hiding this comment

Uh oh!

Sheetal Nandi (sheetalkamat) commented Jan 25, 2019

Uh oh!

Ryan Cavanaugh (RyanCavanaugh) commented Jan 25, 2019

Uh oh!

Anton Lobov (zhuravlikjb) commented Jan 31, 2019

Uh oh!

Anders Hejlsberg (ahejlsberg) commented Jan 31, 2019

Uh oh!

Klaus Meinhardt (ajafff) commented Feb 4, 2019

Uh oh!

falsandtru (falsandtru) commented Feb 4, 2019

Uh oh!

Anders Hejlsberg (ahejlsberg) commented Feb 5, 2019

Uh oh!

falsandtru (falsandtru) commented Feb 5, 2019

Uh oh!

Simon Buchan (simonbuchan) commented Feb 7, 2019

Uh oh!

Felix Becker (felixfbecker) commented Mar 9, 2019

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

12 participants

Improved support for read-only arrays and tuples#29435
Anders Hejlsberg (ahejlsberg) merged 27 commits into
masterfrom
readonlyArrayTuple

Anders Hejlsberg (ahejlsberg) commented Jan 15, 2019 •
edited
Loading