Mixing
Best way to write a constructor that could have invalid parameters
I have a question about writing readable and efficient code in C++.
I’m creating a class for tcp connections with a constructor that takes as input the IP of the server and the port. I would like to avoid the creation of the object if for example the IP is wrong.
My question is:
Is it better to throw an exception in case of a failure or create a
wrapper class with a Boolean to check if the internal object was
created correctly and avoid calling any functions in case of failure?
c++ code-readability
edited Nov 22 '18 at 15:29
scipsycho
1438
asked Nov 22 '18 at 13:44
Matteo CultreraMatteo Cultrera
2311
add a comment |
I have a question about writing readable and efficient code in C++.
I’m creating a class for tcp connections with a constructor that takes as input the IP of the server and the port. I would like to avoid the creation of the object if for example the IP is wrong.
My question is:
Is it better to throw an exception in case of a failure or create a
wrapper class with a Boolean to check if the internal object was
created correctly and avoid calling any functions in case of failure?
c++ code-readability
edited Nov 22 '18 at 15:29
scipsycho
1438
asked Nov 22 '18 at 13:44
Matteo CultreraMatteo Cultrera
2311
4
The "standard" answer to your question. Or you can use factory pattern.
– felix
Nov 22 '18 at 13:46
2
a function that returns astd::optional<connection>if you can use c++17
– user463035818
Nov 22 '18 at 13:50
1
You can also follow wg21.link/p0323 for a possible future option.
– StoryTeller
Nov 22 '18 at 13:54
add a comment |
I have a question about writing readable and efficient code in C++.
I’m creating a class for tcp connections with a constructor that takes as input the IP of the server and the port. I would like to avoid the creation of the object if for example the IP is wrong.
My question is:
Is it better to throw an exception in case of a failure or create a
wrapper class with a Boolean to check if the internal object was
created correctly and avoid calling any functions in case of failure?
c++ code-readability
edited Nov 22 '18 at 15:29
scipsycho
1438
asked Nov 22 '18 at 13:44
Matteo CultreraMatteo Cultrera
2311
I have a question about writing readable and efficient code in C++.
I’m creating a class for tcp connections with a constructor that takes as input the IP of the server and the port. I would like to avoid the creation of the object if for example the IP is wrong.
My question is:
Is it better to throw an exception in case of a failure or create a
wrapper class with a Boolean to check if the internal object was
created correctly and avoid calling any functions in case of failure?
c++ code-readability
c++ code-readability
edited Nov 22 '18 at 15:29
scipsycho
1438
asked Nov 22 '18 at 13:44
Matteo CultreraMatteo Cultrera
2311
edited Nov 22 '18 at 15:29
scipsycho
1438
asked Nov 22 '18 at 13:44
Matteo CultreraMatteo Cultrera
2311
edited Nov 22 '18 at 15:29
scipsycho
1438
edited Nov 22 '18 at 15:29
scipsycho
1438
edited Nov 22 '18 at 15:29
scipsycho
1438
1438
asked Nov 22 '18 at 13:44
Matteo CultreraMatteo Cultrera
2311
asked Nov 22 '18 at 13:44
Matteo CultreraMatteo Cultrera
2311
asked Nov 22 '18 at 13:44
Matteo CultreraMatteo Cultrera
2311
2311
4
The "standard" answer to your question. Or you can use factory pattern.
– felix
Nov 22 '18 at 13:46
2
a function that returns astd::optional<connection>if you can use c++17
– user463035818
Nov 22 '18 at 13:50
1
You can also follow wg21.link/p0323 for a possible future option.
– StoryTeller
Nov 22 '18 at 13:54
add a comment |
4
The "standard" answer to your question. Or you can use factory pattern.
– felix
Nov 22 '18 at 13:46
2
a function that returns astd::optional<connection>if you can use c++17
– user463035818
Nov 22 '18 at 13:50
1
You can also follow wg21.link/p0323 for a possible future option.
– StoryTeller
Nov 22 '18 at 13:54
4
4
The "standard" answer to your question. Or you can use factory pattern.
– felix
Nov 22 '18 at 13:46
The "standard" answer to your question. Or you can use factory pattern.
– felix
Nov 22 '18 at 13:46
2
2
a function that returns a
std::optional<connection> if you can use c++17– user463035818
Nov 22 '18 at 13:50
a function that returns a
std::optional<connection> if you can use c++17– user463035818
Nov 22 '18 at 13:50
1
1
You can also follow wg21.link/p0323 for a possible future option.
– StoryTeller
Nov 22 '18 at 13:54
You can also follow wg21.link/p0323 for a possible future option.
– StoryTeller
Nov 22 '18 at 13:54
add a comment |
1 Answer
1
active
oldest
votes
Throwing in a constructor upon invalid input is fine and even recommend by the core guidelines.
Named constructors (i.e. static member functions) are an equally valid approach, they could e.g. return a std::optional<YourType> (C++17 is required, then). This makes it obvious that the instantiation could fail and circumvents the drawbacks of exceptions. Here's a small example.
#include <optional>
class Example {
public:
static std::optional<Example> validateAndCreate(...);
private:
/* Private ctor makes usage of the above function mandatory. */
Example(...);
};
And an implementation of the creation method could be
std::optional<Example> validateAndCreate(...)
{
/* Use e.g. some utility function for validation: */
if (isInputValid(/* Pass parameter. */))
return Example(/* Pass parameter. */);
else
return std::nullopt;
}
where client code then constructors objects like this:
if (const auto instance = Example::validateAndCreate())
/* Do stuff with the instance. */
;
else
std::cerr << "What now?n";
I guess this approach is more self-documenting (the fact that a ctor might throw should be documented somewhere), but also more verbose.
answered Nov 22 '18 at 13:51
lubgrlubgr
12.7k21847
interesting method indeed. Just one question, does that mean that the variable is always allocated dynamically??
– scipsycho
Nov 22 '18 at 14:08
1
No,std::optionalowns its data and does not allocate. It's like the ordinary return value plus aboolean flag.
– lubgr
Nov 22 '18 at 14:10
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Throwing in a constructor upon invalid input is fine and even recommend by the core guidelines.
Named constructors (i.e. static member functions) are an equally valid approach, they could e.g. return a std::optional<YourType> (C++17 is required, then). This makes it obvious that the instantiation could fail and circumvents the drawbacks of exceptions. Here's a small example.
#include <optional>
class Example {
public:
static std::optional<Example> validateAndCreate(...);
private:
/* Private ctor makes usage of the above function mandatory. */
Example(...);
};
And an implementation of the creation method could be
std::optional<Example> validateAndCreate(...)
{
/* Use e.g. some utility function for validation: */
if (isInputValid(/* Pass parameter. */))
return Example(/* Pass parameter. */);
else
return std::nullopt;
}
where client code then constructors objects like this:
if (const auto instance = Example::validateAndCreate())
/* Do stuff with the instance. */
;
else
std::cerr << "What now?n";
I guess this approach is more self-documenting (the fact that a ctor might throw should be documented somewhere), but also more verbose.
answered Nov 22 '18 at 13:51
lubgrlubgr
12.7k21847
interesting method indeed. Just one question, does that mean that the variable is always allocated dynamically??
– scipsycho
Nov 22 '18 at 14:08
1
No,std::optionalowns its data and does not allocate. It's like the ordinary return value plus aboolean flag.
– lubgr
Nov 22 '18 at 14:10
add a comment |
Throwing in a constructor upon invalid input is fine and even recommend by the core guidelines.
Named constructors (i.e. static member functions) are an equally valid approach, they could e.g. return a std::optional<YourType> (C++17 is required, then). This makes it obvious that the instantiation could fail and circumvents the drawbacks of exceptions. Here's a small example.
#include <optional>
class Example {
public:
static std::optional<Example> validateAndCreate(...);
private:
/* Private ctor makes usage of the above function mandatory. */
Example(...);
};
And an implementation of the creation method could be
std::optional<Example> validateAndCreate(...)
{
/* Use e.g. some utility function for validation: */
if (isInputValid(/* Pass parameter. */))
return Example(/* Pass parameter. */);
else
return std::nullopt;
}
where client code then constructors objects like this:
if (const auto instance = Example::validateAndCreate())
/* Do stuff with the instance. */
;
else
std::cerr << "What now?n";
I guess this approach is more self-documenting (the fact that a ctor might throw should be documented somewhere), but also more verbose.
answered Nov 22 '18 at 13:51
lubgrlubgr
12.7k21847
interesting method indeed. Just one question, does that mean that the variable is always allocated dynamically??
– scipsycho
Nov 22 '18 at 14:08
1
No,std::optionalowns its data and does not allocate. It's like the ordinary return value plus aboolean flag.
– lubgr
Nov 22 '18 at 14:10
add a comment |
Throwing in a constructor upon invalid input is fine and even recommend by the core guidelines.
Named constructors (i.e. static member functions) are an equally valid approach, they could e.g. return a std::optional<YourType> (C++17 is required, then). This makes it obvious that the instantiation could fail and circumvents the drawbacks of exceptions. Here's a small example.
#include <optional>
class Example {
public:
static std::optional<Example> validateAndCreate(...);
private:
/* Private ctor makes usage of the above function mandatory. */
Example(...);
};
And an implementation of the creation method could be
std::optional<Example> validateAndCreate(...)
{
/* Use e.g. some utility function for validation: */
if (isInputValid(/* Pass parameter. */))
return Example(/* Pass parameter. */);
else
return std::nullopt;
}
where client code then constructors objects like this:
if (const auto instance = Example::validateAndCreate())
/* Do stuff with the instance. */
;
else
std::cerr << "What now?n";
I guess this approach is more self-documenting (the fact that a ctor might throw should be documented somewhere), but also more verbose.
answered Nov 22 '18 at 13:51
lubgrlubgr
12.7k21847
Throwing in a constructor upon invalid input is fine and even recommend by the core guidelines.
Named constructors (i.e. static member functions) are an equally valid approach, they could e.g. return a std::optional<YourType> (C++17 is required, then). This makes it obvious that the instantiation could fail and circumvents the drawbacks of exceptions. Here's a small example.
#include <optional>
class Example {
public:
static std::optional<Example> validateAndCreate(...);
private:
/* Private ctor makes usage of the above function mandatory. */
Example(...);
};
And an implementation of the creation method could be
std::optional<Example> validateAndCreate(...)
{
/* Use e.g. some utility function for validation: */
if (isInputValid(/* Pass parameter. */))
return Example(/* Pass parameter. */);
else
return std::nullopt;
}
where client code then constructors objects like this:
if (const auto instance = Example::validateAndCreate())
/* Do stuff with the instance. */
;
else
std::cerr << "What now?n";
I guess this approach is more self-documenting (the fact that a ctor might throw should be documented somewhere), but also more verbose.
answered Nov 22 '18 at 13:51
lubgrlubgr
12.7k21847
answered Nov 22 '18 at 13:51
lubgrlubgr
12.7k21847
answered Nov 22 '18 at 13:51
lubgrlubgr
12.7k21847
answered Nov 22 '18 at 13:51
lubgrlubgr
12.7k21847
12.7k21847
interesting method indeed. Just one question, does that mean that the variable is always allocated dynamically??
– scipsycho
Nov 22 '18 at 14:08
1
No,std::optionalowns its data and does not allocate. It's like the ordinary return value plus aboolean flag.
– lubgr
Nov 22 '18 at 14:10
add a comment |
interesting method indeed. Just one question, does that mean that the variable is always allocated dynamically??
– scipsycho
Nov 22 '18 at 14:08
1
No,std::optionalowns its data and does not allocate. It's like the ordinary return value plus aboolean flag.
– lubgr
Nov 22 '18 at 14:10
interesting method indeed. Just one question, does that mean that the variable is always allocated dynamically??
– scipsycho
Nov 22 '18 at 14:08
interesting method indeed. Just one question, does that mean that the variable is always allocated dynamically??
– scipsycho
Nov 22 '18 at 14:08
1
1
No,
std::optional owns its data and does not allocate. It's like the ordinary return value plus a boolean flag.– lubgr
Nov 22 '18 at 14:10
No,
std::optional owns its data and does not allocate. It's like the ordinary return value plus a boolean flag.– lubgr
Nov 22 '18 at 14:10
add a comment |
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4
The "standard" answer to your question. Or you can use factory pattern.
– felix
Nov 22 '18 at 13:46
2
a function that returns a
std::optional<connection>if you can use c++17– user463035818
Nov 22 '18 at 13:50
1
You can also follow wg21.link/p0323 for a possible future option.
– StoryTeller
Nov 22 '18 at 13:54