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Updated README (#241)
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@mlhaufe
mlhaufe authored Aug 21, 2022
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3 changes: 2 additions & 1 deletion CHANGELOG.md
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## v0.24.1

* Bugfix of generated type declaration (#238)
* Updated README to reflect current features (#)
* Updated README to reflect current features (#239)
* Updated README to use mermaid diagram

## v0.24.0

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80 changes: 51 additions & 29 deletions README.md
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Expand Up @@ -46,15 +46,15 @@ As a dependency run the command:

You can also use a specific [version](https://www.npmjs.com/package/@final-hill/decorator-contracts):

`npm install @final-hill/decorator-contracts@0.23.0`
`npm install @final-hill/decorator-contracts@0.24.1`

For use in a webpage:

`<script src="https://cdn.skypack.dev/@final-hill/decorator-contracts"></script>`

With a specific [version](https://www.npmjs.com/package/@final-hill/decorator-contracts@0.22.0):
With a specific [version](https://www.npmjs.com/package/@final-hill/decorator-contracts@0.24.1):

`<script src="https://cdn.skypack.dev/@final-hill/decorator-contracts@0.23.0"></script>`
`<script src="https://cdn.skypack.dev/@final-hill/decorator-contracts@0.24.1"></script>`

## Usage

Expand Down Expand Up @@ -375,7 +375,7 @@ Note that the current class or one of its ancestors must have `@Contracted(...)`
When assigned, candidate overrides are identified and an
error is raised if an associated `@override` is missing for that feature.

Static methods including the constructor can not be assigned an `@override`
Static methods including the constructor cannot be assigned an `@override`
decorator. In the future this may be enabled for non-constructor static methods
but the implications are not clear at present.

Expand Down Expand Up @@ -502,7 +502,8 @@ const stackContract = new Contract<StackType<any>>({
}
})

class Stack<T> extends Contracted(stackContract) implements StackType<T> {
@Contracted(stackContract)
class Stack<T> implements StackType<T> {
...
pop(): T {
return this.#implementation.pop();
Expand All @@ -517,7 +518,7 @@ In the above example the precondition of executing `pop`
on a stack is that it is not empty. If this assertion fails
an `AssertionError` is raised.

Static features, including the constructor, can not be assigned a `demands`
Static features, including the constructor, cannot be assigned a `demands`
assertion. In the future this may be enabled for non-constructor static methods
but the implications are not clear at present.

Expand Down Expand Up @@ -546,6 +547,7 @@ const baseContract = new Contract<Base>({
})

const subContract = new Contract<Sub>({
[extend]: baseContract,
someMethod: {
demands(){ ... }
}
Expand All @@ -569,6 +571,7 @@ class Base {
}

const subContract = new Contract<Sub>({
[extend]: baseContract,
someMethod: {
demands(_self, x: number){ return -10 <= x && x <= 20 }
}
Expand Down Expand Up @@ -609,7 +612,7 @@ class Stack<T> {

In the above example the post-condition of executing push on a stack is that it is not empty. If this assertion fails an `AssertionError` is raised.

Static features, including the constructor, can not be assigned an `ensures` declaration. In the future this may be enabled for non-constructor static methods but the implications are not clear at present.
Static features, including the constructor, cannot be assigned an `ensures` declaration. In the future this may be enabled for non-constructor static methods but the implications are not clear at present.

In addition to the `self` argument there is also an `old` argument which provides access to the values of any getters of the instance before its associated member was executed.

Expand Down Expand Up @@ -675,13 +678,14 @@ const baseContract = new Contract<Base>({
})

const subContract = new Contract<Sub>({
[extend]: baseContract,
someMethod: {
ensures(){ ... }
}
})
```

This subcontracted `ensures` declaration can not weaken the `ensures` of the base contract. What this means is that the new post-condition will be and-ed with its ancestors. If all of the `ensures` are true then the obligation is considered fulfilled by the author of the feature otherwise an `AssertionError` is raised.
This subcontracted `ensures` declaration cannot weaken the `ensures` of the base contract. What this means is that the new post-condition will be and-ed with its ancestors. If all of the `ensures` are true then the obligation is considered fulfilled by the author of the feature otherwise an `AssertionError` is raised.

```typescript
const baseContract = new Contract<Base>({
Expand All @@ -696,6 +700,7 @@ class Base {
}

const subContract = new Contract<Sub>({
[extend]: baseContract,
method: {
ensures(_self, _old, x: number){ return -10 <= x && x <= 20 }
}
Expand Down Expand Up @@ -799,8 +804,8 @@ const studentRepositoryContract = new Contract<StudentRepository>({
@Contracted(studentRepositoryContract)
class StudentRepository {
...
getStudent(id: string): Student {
const data = fetch(`/repos/students/${id}`).then(response => response.json())
async getStudent(id: string): Student {
const data = await fetch(`/repos/students/${id}`).then(response => response.json())

return new Student(data)
}
Expand Down Expand Up @@ -854,18 +859,18 @@ class AjaxRequest {
get attempts(): number { return this.#attempts }
set attempts(value: number) { this.#attempts = value }

get(url){
get(url) {
if(this.#attempts == 0)
return this.getFetch(url)
else if(this.#attempts == 1)
return this.getXhr(url)
}

getFetch(url) {
async getFetch(url) {
return await fetch(url)
}

getXhr(url) {
async getXhr(url) {
return await new Promise((resolve, reject) => {
const xhr = new XMLHttpRequest();
xhr.open('GET', url);
Expand Down Expand Up @@ -912,7 +917,7 @@ If an error is thrown in the `invariant` then it is raised to the caller.

If an error is thrown in the `demands` then the error is raised to the caller.
In this case the `invariant` is not checked because the feature body has not
been entered and the assertion can not modify the state of the class without
been entered and the assertion cannot modify the state of the class without
calling another method which is governed by its own contracts.

If an error is thrown by the feature body or the `ensures` then
Expand All @@ -922,21 +927,38 @@ starts from the beginning.
If `rescue` throws an error or does not call `retry` then the
`invariant` is checked before the error is raised to the caller.

```ts
(error) <-----------------+
^ (throws) | (throws)
| |
obj.feature(...) -> @invariant -> @demands -> { feature body } --+
^ | |
| | (throws) |
| (retry) | | (return)
+------------ @rescue <---+------+ |
| | |
| (throws|return) | |
(error) <--- @invariant <-+ | |
| (throws) |
| |
(return) <-- @invariant <---------------- @ensures <------+
```mermaid
flowchart LR
Feature(("obj.feature(...)"))
Invariant["@invariant"]
Invariant2["@invariant"]
Invariant3["@invariant"]
Demands["@demands"]
Ensures["@ensures"]
Rescue["@rescue"]
Error(("Error"))
Body["{feature body}"]
Result(("Result"))
Feature --> Invariant
Invariant -->|throws| Error
Invariant --> Demands
Demands -->|throws| Error
Demands --> Body
Body -->|throws| Rescue
Rescue -->|retry| Invariant
Body -->|returns| Ensures
Ensures -->|throws| Rescue
Ensures --> Invariant3
Invariant3 --> Result
Rescue --> |throws| Invariant2
Rescue --> |returns| Invariant2
Invariant2 --> Error
style Error fill:red
style Result fill:green
style Rescue fill:darkorange
```

## Further Reading
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