Only class objects can be a type

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I have part of a question that I cannot understand. I am supposed to modify code so that only class objects (objects that have constructors) can be a type. I don't understand what the second part of the question means, so here is my question:

Are there instances when ONLY class objects are allowed as types? If so, what are they?

What I have tried:

I have tried Google, looking through my notes, and looking through my text book

Posted 11-Dec-17 17:25pm

Member 13567385

Updated 11-Dec-17 21:25pm

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________________ 12-Dec-17 2:07am

Each "programming thing (byte as smallest store unit)" has its own address in RAM (Random Assess Memory).
So, the problem how to store more than 1 byte was solved by defining "types of data" in high-level languages.
Simple types - integer for example, was converted to full stack class in .NET (and it has methods "ToString()"), but remains simple pointer to address of first byte in C++ or Java.

For programmer - "type" is only definition of how to save-read data from memory.
"Instance" - it is real place in memory, occupied by data.

________________ 12-Dec-17 2:12am

So, in you sentence- "Class" - it is "Type" because it is not simple type - as integer, byte....
Correct meaning depends of what are we speaking about - Java, C, C++, C#....

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OriginalGriff · Answer 1 · 2017-12-11T20:04:00

I assume you mean in a Generic method or class:

C#

public T MyGenericMethod<T>(T myParameter)
   {
   ... 
   }

If so, then yes, it's pretty easy to restrict the class type to those with a constructor:

C#

public T MyGenericMethod<T>(T myParameter) where T: new()
   {
   ... 
   }

Unless the class you use the method with is a concrete class which has a public parameterless constructor, you will get an error.

If that isn't what you are trying to find out about, you will have to explain yourself in much greater detail.

CPallini · Answer 2 · 2017-12-11T21:24:00

Solution 2

There are programming languages where every instance variable is an object of a class (and the class represents its type). They are called pure OOP languages. An example is smalltalk. C# and Java, for instance, are NOT pure OOP languages.

Posted 11-Dec-17 21:24pm

CPallini