why is asDictonary a class method
Hello, Im busy with a new challenge from exercism. Where I have to keep track of a robot , where it facing and on that coordinate the robot is. so I made this function what the test wanted createDirection: aString position: aCollection    self robot: (Robot directionLooking: aString) yourself.    ^ self robot asDictonary I can see that on the first part a new robot is made with the right data. but the test wants the data back as a Dictonary that is why I made the self robot asDictonary line but to my suprise the compiler wants it be a class method where I expect it to be a instance method. Can someone explain to my why this is ? Roelof
Didn't you forget to return (^) an instance from #directionLooking:? And why do you need to send #yourself? Ñб, 30 маÑÑа 2019 г. в 21:19, Roelof Wobben <r.wobben@home.nl>:
Hello,
Im busy with a new challenge from exercism. Where I have to keep track of a robot , where it facing and on that coordinate the robot is.
so I made this function what the test wanted
createDirection: aString position: aCollection self robot: (Robot directionLooking: aString) yourself. ^ self robot asDictonary
I can see that on the first part a new robot is made with the right data. but the test wants the data back as a Dictonary that is why I made the self robot asDictonary line
but to my suprise the compiler wants it be a class method where I expect it to be a instance method.
Can someone explain to my why this is ?
Roelof
--
-- Best regards, Dennis Schetinin
Question 1. Should that be #asDictionary? Question 2. If not, what's a Dictonary? Question 3. I see you are using self-encapsulation, with a getter 'self robot' and a setter 'self robot: something'. Of course that means that outside code can freely smash your "robot" property, unless #robot: checks that its argument makes sense. Does it? Question 4. What kind of thing *is* "robot". Have you checked that 'Robot directionLooking: ...' returns an instance of Robot? If you accidentally omitted '^' it might return the Robot class itself. Question 5. Are you sure that 'self robot' returns what you think it does? Have you checked? Question 6. Does Robot have an #asDictionary method? Does Robot have an #asDictonary method? Question 7. Why is "aCollection" not used in this method? Question 8. Why are you using 'yourself'? Question 9. Why does the caller want a dictionary instead of a Robot? What should be in that dictionary? There are more questions but those will do to be going on with. If your #robot: method began like robot: aRobot (aRobot isKindOf: Robot) ifFalse: [aRobot error: 'not an instance of Robot']. you would have caught what I suspect is your problem. Check question 4. On Sun, 31 Mar 2019 at 07:19, Roelof Wobben <r.wobben@home.nl> wrote:
Hello,
Im busy with a new challenge from exercism. Where I have to keep track of a robot , where it facing and on that coordinate the robot is.
so I made this function what the test wanted
createDirection: aString position: aCollection self robot: (Robot directionLooking: aString) yourself. ^ self robot asDictonary
I can see that on the first part a new robot is made with the right data. but the test wants the data back as a Dictonary that is why I made the self robot asDictonary line
but to my suprise the compiler wants it be a class method where I expect it to be a instance method.
Can someone explain to my why this is ?
Roelof
I think you probably need to show us *all* the code. directionLooking: aString self new direction: aString Well, there is your problem. There are two ways for a method to return a value. One is to execute '^ e' for some expression e, which is quite like a 'return e;' statement in C. The other is to execute the whole body and come to the end of the method, and in that case the result is always 'self'. This means that the method as you wrote it - created an uninitialised or incompletely initialised instance of Robot (self new) - asked that instance to set its direction - discarded the result of that setting - forgot the new instance - returned the Robot class What you probably meant was directionLooking: aString ^(self new) direction: aString; yourself where 'yourself' has nothing to do with a new object being created but with the fact that you want the new object as the result, not whatever #direction: returns. directionLooking: aString |newRobot| newRobot := self new. newRobot direction: aString. ^newRobot may be clearer to you. By the way, you didn't say WHY the caller wants a Dictionary instead of a Robot. I don't think I've ever written a program where that was a good idea. On Sun, 31 Mar 2019 at 19:55, Roelof Wobben <r.wobben@home.nl> wrote:
Op 31-3-2019 om 03:47 schreef Richard O'Keefe:
Question 1. Should that be #asDictionary?
yes, it does.
Question 2. If not, what's a Dictonary? Question 3. I see you are using self-encapsulation, with a getter 'self robot' and a setter 'self robot: something'. Of course that means that outside code can freely smash your "robot" property, unless #robot: checks that its argument makes sense. Does it?
no, it does not.
Question 4. What kind of thing *is* "robot". Have you checked that 'Robot directionLooking: ...' returns an instance of Robot? If you accidentally omitted '^' it might return the Robot class itself.
yes, I forget the ^ thing see this code.
directionLooking: aString self new direction: aString
so I have to think well how to return a instance of a Robot here.
as far as I see I do not have a robot yet.
createDirection: aString position: aCollection self robot: (Robot directionLooking: aString) yourself. ^ self robot asDictionary
or I overlook something.
Question 5. Are you sure that 'self robot' returns what you think it does? Have you checked?
yes, I checked. self Robot give me a variable robot which is a Robot.
Question 6. Does Robot have an #asDictionary method? Does Robot have an #asDictonary method?
Yes, it does
Question 7. Why is "aCollection" not used in this method?
Because I wanted to be sure things are working before I added the position which is a difficult one.
Question 8. Why are you using 'yourself'?
I thought I was needed so I get a instance of a Robot back.
Question 9. Why does the caller want a dictionary instead of a Robot? What should be in that dictionary?
The same data as the Robot has but then in a dictionary form. That is what I try to achieve.
There are more questions but those will do to be going on with. If your #robot: method began like robot: aRobot (aRobot isKindOf: Robot) ifFalse: [aRobot error: 'not an instance of Robot']. you would have caught what I suspect is your problem. Check question 4.
On Sun, 31 Mar 2019 at 07:19, Roelof Wobben <r.wobben@home.nl> wrote:
Hello,
Im busy with a new challenge from exercism. Where I have to keep track of a robot , where it facing and on that coordinate the robot is.
so I made this function what the test wanted
createDirection: aString position: aCollection self robot: (Robot directionLooking: aString) yourself. ^ self robot asDictonary
I can see that on the first part a new robot is made with the right data. but the test wants the data back as a Dictonary that is why I made the self robot asDictonary line
but to my suprise the compiler wants it be a class method where I expect it to be a instance method.
Can someone explain to my why this is ?
Roelof
Hi Richard/all - thanks for helping Roelof out. Heâs working through the exercism.io exercises that weâve managed to convert so far. As they are based on more C like languages, they arenât always as OO as we want (once we get a decent set converted, weâll try and add some smallish examples - anyoneâs favourites appreciated). The dictionary reference is normally because the exercise tests like to assert on some description at the end (and dictionaries tend to exist universally in most languages). So view it more as a #printOn: like finalé (this said - Roelof might have this behaviour in the wrong place - but we will see). The feedback so far, seems to have helpfully unblocked him so thanks all. Tim Sent from my iPhone
On 31 Mar 2019, at 12:02, Richard O'Keefe <raoknz@gmail.com> wrote:
I think you probably need to show us *all* the code.
directionLooking: aString self new direction: aString
Well, there is your problem. There are two ways for a method to return a value. One is to execute '^ e' for some expression e, which is quite like a 'return e;' statement in C. The other is to execute the whole body and come to the end of the method, and in that case the result is always 'self'. This means that the method as you wrote it - created an uninitialised or incompletely initialised instance of Robot (self new) - asked that instance to set its direction - discarded the result of that setting - forgot the new instance - returned the Robot class
What you probably meant was directionLooking: aString ^(self new) direction: aString; yourself where 'yourself' has nothing to do with a new object being created but with the fact that you want the new object as the result, not whatever #direction: returns. directionLooking: aString |newRobot| newRobot := self new. newRobot direction: aString. ^newRobot may be clearer to you.
By the way, you didn't say WHY the caller wants a Dictionary instead of a Robot. I don't think I've ever written a program where that was a good idea.
On Sun, 31 Mar 2019 at 19:55, Roelof Wobben <r.wobben@home.nl> wrote: Op 31-3-2019 om 03:47 schreef Richard O'Keefe:
Question 1. Should that be #asDictionary?
yes, it does.
Question 2. If not, what's a Dictonary? Question 3. I see you are using self-encapsulation, with a getter 'self robot' and a setter 'self robot: something'. Of course that means that outside code can freely smash your "robot" property, unless #robot: checks that its argument makes sense. Does it?
no, it does not.
Question 4. What kind of thing *is* "robot". Have you checked that 'Robot directionLooking: ...' returns an instance of Robot? If you accidentally omitted '^' it might return the Robot class itself.
yes, I forget the ^ thing see this code.
directionLooking: aString self new direction: aString
so I have to think well how to return a instance of a Robot here.
as far as I see I do not have a robot yet.
createDirection: aString position: aCollection self robot: (Robot directionLooking: aString) yourself. ^ self robot asDictionary
or I overlook something.
Question 5. Are you sure that 'self robot' returns what you think it does? Have you checked?
yes, I checked. self Robot give me a variable robot which is a Robot.
Question 6. Does Robot have an #asDictionary method? Does Robot have an #asDictonary method?
Yes, it does
Question 7. Why is "aCollection" not used in this method?
Because I wanted to be sure things are working before I added the position which is a difficult one.
Question 8. Why are you using 'yourself'?
I thought I was needed so I get a instance of a Robot back.
Question 9. Why does the caller want a dictionary instead of a Robot? What should be in that dictionary?
The same data as the Robot has but then in a dictionary form. That is what I try to achieve.
There are more questions but those will do to be going on with. If your #robot: method began like robot: aRobot (aRobot isKindOf: Robot) ifFalse: [aRobot error: 'not an instance of Robot']. you would have caught what I suspect is your problem. Check question 4.
On Sun, 31 Mar 2019 at 07:19, Roelof Wobben <r.wobben@home.nl> wrote: Hello,
Im busy with a new challenge from exercism. Where I have to keep track of a robot , where it facing and on that coordinate the robot is.
so I made this function what the test wanted
createDirection: aString position: aCollection self robot: (Robot directionLooking: aString) yourself. ^ self robot asDictonary
I can see that on the first part a new robot is made with the right data. but the test wants the data back as a Dictonary that is why I made the self robot asDictonary line
but to my suprise the compiler wants it be a class method where I expect it to be a instance method.
Can someone explain to my why this is ?
Roelof
participants (4)
-
Dennis Schetinin -
Richard O'Keefe -
Roelof Wobben -
Tim Mackinnon