Prevent duplication of fields in child class
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2
class Parent {
// how can we decorate this field to
// prevent duplication in the child?
readonly name: string;
}
class Child extends Parent {
readonly name: string;
}
That is the kind of scenario I would like to cause a compiler error.
Edit
This is the scenario that occurs when running the code with babel-jest.
class Parent {
readonly name: string;
constructor() {
this.name = 'foo';
}
}
class Child extends Parent {
readonly name: string;
constructor() {
super();
}
}
const child = new Child();
document.writeln(child.name); // undefined
typescript
asked Nov 17 '18 at 0:52
Shaun LuttinShaun Luttin
63.5k36238299
add a comment |
2
class Parent {
// how can we decorate this field to
// prevent duplication in the child?
readonly name: string;
}
class Child extends Parent {
readonly name: string;
}
That is the kind of scenario I would like to cause a compiler error.
Edit
This is the scenario that occurs when running the code with babel-jest.
class Parent {
readonly name: string;
constructor() {
this.name = 'foo';
}
}
class Child extends Parent {
readonly name: string;
constructor() {
super();
}
}
const child = new Child();
document.writeln(child.name); // undefined
typescript
asked Nov 17 '18 at 0:52
Shaun LuttinShaun Luttin
63.5k36238299
Why would you want this behavior?
– Nurbol Alpysbayev
Nov 17 '18 at 3:51
I was running into trouble, when compiling with Babel, in which the child class'snameproperty was undefined, even though the parent class had set its value. @NurbolAlpysbayev
– Shaun Luttin
Nov 17 '18 at 3:59
@ShaunLuttin can you create an example case?
– Katie.Sun
Nov 17 '18 at 4:00
I can give it shot... we need an online TypeScript/Babel repl.
– Shaun Luttin
Nov 17 '18 at 4:02
add a comment |
2
2
2
2
class Parent {
// how can we decorate this field to
// prevent duplication in the child?
readonly name: string;
}
class Child extends Parent {
readonly name: string;
}
That is the kind of scenario I would like to cause a compiler error.
Edit
This is the scenario that occurs when running the code with babel-jest.
class Parent {
readonly name: string;
constructor() {
this.name = 'foo';
}
}
class Child extends Parent {
readonly name: string;
constructor() {
super();
}
}
const child = new Child();
document.writeln(child.name); // undefined
typescript
asked Nov 17 '18 at 0:52
Shaun LuttinShaun Luttin
63.5k36238299
class Parent {
// how can we decorate this field to
// prevent duplication in the child?
readonly name: string;
}
class Child extends Parent {
readonly name: string;
}
That is the kind of scenario I would like to cause a compiler error.
Edit
This is the scenario that occurs when running the code with babel-jest.
class Parent {
readonly name: string;
constructor() {
this.name = 'foo';
}
}
class Child extends Parent {
readonly name: string;
constructor() {
super();
}
}
const child = new Child();
document.writeln(child.name); // undefined
typescript
typescript
asked Nov 17 '18 at 0:52
Shaun LuttinShaun Luttin
63.5k36238299
asked Nov 17 '18 at 0:52
Shaun LuttinShaun Luttin
63.5k36238299
edited Nov 17 '18 at 4:05
Shaun Luttin
asked Nov 17 '18 at 0:52
Shaun LuttinShaun Luttin
63.5k36238299
asked Nov 17 '18 at 0:52
Shaun LuttinShaun Luttin
63.5k36238299
asked Nov 17 '18 at 0:52
Shaun LuttinShaun Luttin
63.5k36238299
63.5k36238299
Why would you want this behavior?
– Nurbol Alpysbayev
Nov 17 '18 at 3:51
I was running into trouble, when compiling with Babel, in which the child class'snameproperty was undefined, even though the parent class had set its value. @NurbolAlpysbayev
– Shaun Luttin
Nov 17 '18 at 3:59
@ShaunLuttin can you create an example case?
– Katie.Sun
Nov 17 '18 at 4:00
I can give it shot... we need an online TypeScript/Babel repl.
– Shaun Luttin
Nov 17 '18 at 4:02
add a comment |
Why would you want this behavior?
– Nurbol Alpysbayev
Nov 17 '18 at 3:51
I was running into trouble, when compiling with Babel, in which the child class'snameproperty was undefined, even though the parent class had set its value. @NurbolAlpysbayev
– Shaun Luttin
Nov 17 '18 at 3:59
@ShaunLuttin can you create an example case?
– Katie.Sun
Nov 17 '18 at 4:00
I can give it shot... we need an online TypeScript/Babel repl.
– Shaun Luttin
Nov 17 '18 at 4:02
Why would you want this behavior?
– Nurbol Alpysbayev
Nov 17 '18 at 3:51
Why would you want this behavior?
– Nurbol Alpysbayev
Nov 17 '18 at 3:51
I was running into trouble, when compiling with Babel, in which the child class's
name property was undefined, even though the parent class had set its value. @NurbolAlpysbayev– Shaun Luttin
Nov 17 '18 at 3:59
I was running into trouble, when compiling with Babel, in which the child class's
name property was undefined, even though the parent class had set its value. @NurbolAlpysbayev– Shaun Luttin
Nov 17 '18 at 3:59
@ShaunLuttin can you create an example case?
– Katie.Sun
Nov 17 '18 at 4:00
@ShaunLuttin can you create an example case?
– Katie.Sun
Nov 17 '18 at 4:00
I can give it shot... we need an online TypeScript/Babel repl.
– Shaun Luttin
Nov 17 '18 at 4:02
I can give it shot... we need an online TypeScript/Babel repl.
– Shaun Luttin
Nov 17 '18 at 4:02
add a comment |
1 Answer
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There is no such solution (and shouldn't be?), probably because it contradicts with OOP principles like open-closed principle.
There is a workaround, though (with trade-offs as always).
Make a property private
class Parent {
private name: string = '';
}
this way the property in child class would cause compilation error "Types have separate declarations of a private property"
answered Nov 17 '18 at 3:50
Nurbol AlpysbayevNurbol Alpysbayev
4,9191634
Nice concept, but aren't child classes inherently modifications of their parents?
– Katie.Sun
Nov 17 '18 at 4:00
@Katie.Sun Sorry, didn't get your point.
– Nurbol Alpysbayev
Nov 17 '18 at 4:06
It's kind of philosophical, but what I was trying to get at is that the notion of child class that doesn't modify its parent is nonexistent. The existence of a child class is a modification of a parent class. But hey, I'm here to learn. School me
– Katie.Sun
Nov 17 '18 at 4:13
Your american english is a bit hard for me, but if I got you correctly, you are generally correct, child should always be able to extend, i.e. modify properties of properties (makes sense?) of parent class. However, I am no good teacher for this subject, I ain't got even CS degree. So you should read the wikipedia article instead ;) I am more like a practice-guy
– Nurbol Alpysbayev
Nov 17 '18 at 4:21
Haha ok. I mean I get the concept I just think it's a bit of Baloney. If I knew the equivalent of Baloney I would try to find it in your language :)
– Katie.Sun
Nov 17 '18 at 4:23
|
show 1 more comment
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
0
There is no such solution (and shouldn't be?), probably because it contradicts with OOP principles like open-closed principle.
There is a workaround, though (with trade-offs as always).
Make a property private
class Parent {
private name: string = '';
}
this way the property in child class would cause compilation error "Types have separate declarations of a private property"
answered Nov 17 '18 at 3:50
Nurbol AlpysbayevNurbol Alpysbayev
4,9191634
Nice concept, but aren't child classes inherently modifications of their parents?
– Katie.Sun
Nov 17 '18 at 4:00
@Katie.Sun Sorry, didn't get your point.
– Nurbol Alpysbayev
Nov 17 '18 at 4:06
It's kind of philosophical, but what I was trying to get at is that the notion of child class that doesn't modify its parent is nonexistent. The existence of a child class is a modification of a parent class. But hey, I'm here to learn. School me
– Katie.Sun
Nov 17 '18 at 4:13
Your american english is a bit hard for me, but if I got you correctly, you are generally correct, child should always be able to extend, i.e. modify properties of properties (makes sense?) of parent class. However, I am no good teacher for this subject, I ain't got even CS degree. So you should read the wikipedia article instead ;) I am more like a practice-guy
– Nurbol Alpysbayev
Nov 17 '18 at 4:21
Haha ok. I mean I get the concept I just think it's a bit of Baloney. If I knew the equivalent of Baloney I would try to find it in your language :)
– Katie.Sun
Nov 17 '18 at 4:23
|
show 1 more comment
0
There is no such solution (and shouldn't be?), probably because it contradicts with OOP principles like open-closed principle.
There is a workaround, though (with trade-offs as always).
Make a property private
class Parent {
private name: string = '';
}
this way the property in child class would cause compilation error "Types have separate declarations of a private property"
answered Nov 17 '18 at 3:50
Nurbol AlpysbayevNurbol Alpysbayev
4,9191634
Nice concept, but aren't child classes inherently modifications of their parents?
– Katie.Sun
Nov 17 '18 at 4:00
@Katie.Sun Sorry, didn't get your point.
– Nurbol Alpysbayev
Nov 17 '18 at 4:06
It's kind of philosophical, but what I was trying to get at is that the notion of child class that doesn't modify its parent is nonexistent. The existence of a child class is a modification of a parent class. But hey, I'm here to learn. School me
– Katie.Sun
Nov 17 '18 at 4:13
Your american english is a bit hard for me, but if I got you correctly, you are generally correct, child should always be able to extend, i.e. modify properties of properties (makes sense?) of parent class. However, I am no good teacher for this subject, I ain't got even CS degree. So you should read the wikipedia article instead ;) I am more like a practice-guy
– Nurbol Alpysbayev
Nov 17 '18 at 4:21
Haha ok. I mean I get the concept I just think it's a bit of Baloney. If I knew the equivalent of Baloney I would try to find it in your language :)
– Katie.Sun
Nov 17 '18 at 4:23
|
show 1 more comment
0
0
0
There is no such solution (and shouldn't be?), probably because it contradicts with OOP principles like open-closed principle.
There is a workaround, though (with trade-offs as always).
Make a property private
class Parent {
private name: string = '';
}
this way the property in child class would cause compilation error "Types have separate declarations of a private property"
answered Nov 17 '18 at 3:50
Nurbol AlpysbayevNurbol Alpysbayev
4,9191634
There is no such solution (and shouldn't be?), probably because it contradicts with OOP principles like open-closed principle.
There is a workaround, though (with trade-offs as always).
Make a property private
class Parent {
private name: string = '';
}
this way the property in child class would cause compilation error "Types have separate declarations of a private property"
answered Nov 17 '18 at 3:50
Nurbol AlpysbayevNurbol Alpysbayev
4,9191634
edited Nov 17 '18 at 4:05
answered Nov 17 '18 at 3:50
Nurbol AlpysbayevNurbol Alpysbayev
4,9191634
answered Nov 17 '18 at 3:50
Nurbol AlpysbayevNurbol Alpysbayev
4,9191634
answered Nov 17 '18 at 3:50
Nurbol AlpysbayevNurbol Alpysbayev
4,9191634
4,9191634
Nice concept, but aren't child classes inherently modifications of their parents?
– Katie.Sun
Nov 17 '18 at 4:00
@Katie.Sun Sorry, didn't get your point.
– Nurbol Alpysbayev
Nov 17 '18 at 4:06
It's kind of philosophical, but what I was trying to get at is that the notion of child class that doesn't modify its parent is nonexistent. The existence of a child class is a modification of a parent class. But hey, I'm here to learn. School me
– Katie.Sun
Nov 17 '18 at 4:13
Your american english is a bit hard for me, but if I got you correctly, you are generally correct, child should always be able to extend, i.e. modify properties of properties (makes sense?) of parent class. However, I am no good teacher for this subject, I ain't got even CS degree. So you should read the wikipedia article instead ;) I am more like a practice-guy
– Nurbol Alpysbayev
Nov 17 '18 at 4:21
Haha ok. I mean I get the concept I just think it's a bit of Baloney. If I knew the equivalent of Baloney I would try to find it in your language :)
– Katie.Sun
Nov 17 '18 at 4:23
|
show 1 more comment
Nice concept, but aren't child classes inherently modifications of their parents?
– Katie.Sun
Nov 17 '18 at 4:00
@Katie.Sun Sorry, didn't get your point.
– Nurbol Alpysbayev
Nov 17 '18 at 4:06
It's kind of philosophical, but what I was trying to get at is that the notion of child class that doesn't modify its parent is nonexistent. The existence of a child class is a modification of a parent class. But hey, I'm here to learn. School me
– Katie.Sun
Nov 17 '18 at 4:13
Your american english is a bit hard for me, but if I got you correctly, you are generally correct, child should always be able to extend, i.e. modify properties of properties (makes sense?) of parent class. However, I am no good teacher for this subject, I ain't got even CS degree. So you should read the wikipedia article instead ;) I am more like a practice-guy
– Nurbol Alpysbayev
Nov 17 '18 at 4:21
Haha ok. I mean I get the concept I just think it's a bit of Baloney. If I knew the equivalent of Baloney I would try to find it in your language :)
– Katie.Sun
Nov 17 '18 at 4:23
Nice concept, but aren't child classes inherently modifications of their parents?
– Katie.Sun
Nov 17 '18 at 4:00
Nice concept, but aren't child classes inherently modifications of their parents?
– Katie.Sun
Nov 17 '18 at 4:00
@Katie.Sun Sorry, didn't get your point.
– Nurbol Alpysbayev
Nov 17 '18 at 4:06
@Katie.Sun Sorry, didn't get your point.
– Nurbol Alpysbayev
Nov 17 '18 at 4:06
It's kind of philosophical, but what I was trying to get at is that the notion of child class that doesn't modify its parent is nonexistent. The existence of a child class is a modification of a parent class. But hey, I'm here to learn. School me
– Katie.Sun
Nov 17 '18 at 4:13
It's kind of philosophical, but what I was trying to get at is that the notion of child class that doesn't modify its parent is nonexistent. The existence of a child class is a modification of a parent class. But hey, I'm here to learn. School me
– Katie.Sun
Nov 17 '18 at 4:13
Your american english is a bit hard for me, but if I got you correctly, you are generally correct, child should always be able to extend, i.e. modify properties of properties (makes sense?) of parent class. However, I am no good teacher for this subject, I ain't got even CS degree. So you should read the wikipedia article instead ;) I am more like a practice-guy
– Nurbol Alpysbayev
Nov 17 '18 at 4:21
Your american english is a bit hard for me, but if I got you correctly, you are generally correct, child should always be able to extend, i.e. modify properties of properties (makes sense?) of parent class. However, I am no good teacher for this subject, I ain't got even CS degree. So you should read the wikipedia article instead ;) I am more like a practice-guy
– Nurbol Alpysbayev
Nov 17 '18 at 4:21
Haha ok. I mean I get the concept I just think it's a bit of Baloney. If I knew the equivalent of Baloney I would try to find it in your language :)
– Katie.Sun
Nov 17 '18 at 4:23
Haha ok. I mean I get the concept I just think it's a bit of Baloney. If I knew the equivalent of Baloney I would try to find it in your language :)
– Katie.Sun
Nov 17 '18 at 4:23
|
show 1 more comment
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Why would you want this behavior?
– Nurbol Alpysbayev
Nov 17 '18 at 3:51
I was running into trouble, when compiling with Babel, in which the child class's
nameproperty was undefined, even though the parent class had set its value. @NurbolAlpysbayev– Shaun Luttin
Nov 17 '18 at 3:59
@ShaunLuttin can you create an example case?
– Katie.Sun
Nov 17 '18 at 4:00
I can give it shot... we need an online TypeScript/Babel repl.
– Shaun Luttin
Nov 17 '18 at 4:02