Skipping Optional Positional Arguments

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Stewart
Stewart 2024-10-25，22:36
回答： 埃博拉酱 2024-10-26，15:02
I am writing a routine that uses arguments to parse input parameters. After many years of using both inputParser and manual input parsing, I like using arguments. However, I seem to be running into some limitations.
I am trying to get arguments to ignore an optional positional arguments. Take the example function:
function y = foo(a,b,c)
arguments
a
b = 2
c = 3
end
y = a + b + c;
end
Suppose I want to specify arguments for a and c and use the default value of b. With manual parsing, I would just detect an empty value for b by calling foo(1,[],3). When using arguments, I can not achieve the same functionality by calling as foo(1,~,3) or similar syntax.
Is there a way to get this functionality without resorting to manual parsing?
  2 个评论
Stephen23
Stephen23 2024-10-25，23:27
"Is there a way to get this functionality without resorting to manual parsing?"
Not as far as I am aware. You should make an enhancement suggestion here:
https://www.mathworks.com/support/contact_us.html
Stewart
Stewart 2024-10-26，2:35
Just went ahead and created an enhacement suggestion. I wanted to check to see if I was missing a simple workaround, the timeline for getting this into a release definitely won't be quick.

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回答（3 个）

Star Strider
Star Strider 2024-10-25，23:36
Ran in:
I usually use varargin rather than arguments, however your calling syntax may not be appropriate
To illustrate —
out = foo(1,pi,3)
out = 7.1416
out = foo(1,[],3)
out = 6
out = foo(1,~,3)
Using ~ in this context is not supported.
function y = foo(a,varargin)
optargs = cell(1,2);
optargs(1:numel(varargin)) = varargin;
if isempty(optargs{1})
b = 2;
else
b = optargs{1};
end
if isempty(optargs{2})
c = 3;
else
c = optargs{2};
end
y = a + b + c;
end
Not everything is possible.
.
Walter Roberson
Walter Roberson 2024-10-26，3:53
Unfortunately you cannot use [] to trigger detection as "missing" for the purpose of default argument processing.
function y = foo(a,b,c)
arguments
a
b double {mustBeEmptyOrNumeric(b)} = 2
c = 3
end
if isempty(b); b = 2; end
y = a + b + c;
end
function mustBeEmptyOrNumeric(b)
if ~isempty(b) && ~isnumeric(b)
eidType = 'mustBeEmptyOrNumeric:notEmptyOrNumeric';
msgType = 'Input must be empty or numeric.';
error(eidType, msgType);
end
end
埃博拉酱
埃博拉酱 2024-10-26，15:02
It is recommended that you use name-value arguments:
function y = foo(a,options)
arguments
a
options.b = 2
options.c = 3
end
y = a + b + c;
end
Then you can specify c without b:
foo(1,c=3);

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