How to set a default value to a map container in argument validation?

Question

Anup Kanale 2023-3-27

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1936099-how-to-set-a-default-value-to-a-map-container-in-argument-validation

移动：Walter Roberson 2023-4-4

I'm validating a bunch of arguments in class properties. Seems quite straightfoward to set a deatault for double, integer and string datatypes.

classdef newClass < handle
    
    properties
        someStr (1,:) string = "myStr"
        someNum (1,1) double = 3.1415
    end

But what is the right way to do this for a map container? Because when I add this line for a map container:

someDict containers.Map

I see the following warning:

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Steven Lord 2023-3-30

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1936099-how-to-set-a-default-value-to-a-map-container-in-argument-validation#answer_1208979

移动：Walter Roberson 2023-4-4

在 MATLAB Online 中打开

Because each function call is independent I'd expect you wouldn't have the same issue with a handle object in a function's arguments block that you would with a class's properties block. Indeed, this little experiment supports my expectation. If the default value for dict was only created once the second call to the function should have listed both oldMissingValue and myKey as keys of the dict variable.

listOfKeys = example1936099_arg(42, "myKey")
listOfKeys = 1×1 cell array
    {'myKey'}
listOfKeys = example1936099_arg(-999, "oldMissingValue")
listOfKeys = 1×1 cell array
    {'oldMissingValue'}
listOfKeys = example1936099_arg()
listOfKeys = 1×1 cell array
    {'myStr'}
function listOfKeys = example1936099_arg(value, name, dict)
arguments
    value (1, 1) double = pi;
    name (1, :) string = "myStr";
    dict containers.Map = containers.Map;
end
dict(name) = value;
listOfKeys = keys(dict);
end

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Anup Kanale 2023-4-4

移动：Walter Roberson 2023-4-4

Thank you Steven, this answers my question! If you could move this to Answer, I'll accept it.

请先登录，再进行评论。

Answer 2

Walter Roberson 2023-3-27

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1936099-how-to-set-a-default-value-to-a-map-container-in-argument-validation#answer_1202119

在 MATLAB Online 中打开

test = containers.Map

test = Map with properties: Count: 0 KeyType: char ValueType: any

isa(test, 'handle')

ans = logical

1

Therefore if you were to pass in a container.Map to the constructor and copy what was received into a property, then the container would end up being shared with any other uses of the container.

To get around this, to get a private container.Map, you need to create the container.Map in the constructor (and make the property private and do not create any methods that can allow people to get at the container.Map). Or you could somehow clone the incoming container.Map (the class does not provide a method for copying / cloning though.)

If you want the container.Map to be shared then mark the property as Constant .

6 个评论
显示 4更早的评论隐藏 4更早的评论

Anup Kanale 2023-3-28

在 MATLAB Online 中打开

I want a private copy of the container. But my bad, your and @Steven Lord's answers made me realize that I am probably mixing up two different issues in my head! The first one is shared vs private copy of the container.

The second issue, and what I originally meant to ask, was how do I go about setting a default value for a container in the argument validation block (it makes sense in my script to move the container downstream from class property to a method)

function returnVar=myFunc(someNum, someStr, someDict)
    arguments
        someNum (1,1) double = 3.1415
        someStr (1,:) string = "myStr"
        someDict containers.Map = %?__default_value__?
    end 
end

PS: For the future viewer's benefit, please let me know if I should modify this question in place, or start a new thread instead.

Walter Roberson 2023-3-30

Sorry, I do not have experience with using arguments blocks.

请先登录，再进行评论。

Answer 3

Steven Lord 2023-3-27

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1936099-how-to-set-a-default-value-to-a-map-container-in-argument-validation#answer_1202159

在 MATLAB Online 中打开

Consider the two classes attached to this answer. The class class1936099_A defines someDict to contain a containers.Map in the properties section of the class definition. The class class1936099_B assigns someDict a containers.Map in the constructor.

obj1 = class1936099_A;
obj2 = class1936099_A;

Neither obj1 nor obj2 have 'a' as a key in their someDict property.

[isKey(obj1.someDict, 'a'), isKey(obj2.someDict, 'a')]
ans = 1×2 logical array
   0   0

Let's associate 'a' with 42 in obj1's property. What does obj2's property associate 'a' with now?

obj1.someDict('a') = 42;
obj2.someDict('a')
ans = 42

Let's try the same with class1936099_B.

obj3 = class1936099_B;
obj4 = class1936099_B;
[isKey(obj3.someDict, 'a'), isKey(obj4.someDict, 'a')]
ans = 1×2 logical array
   0   0
obj3.someDict('a') = 42;
obj4.someDict('a')
Error using indexing
The specified key is not present in this container.