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What is the usefulness of `enable_shared_from_this`?
(6 answers)
Closed 5 years ago.
What is the point for a class T to inherit from std::enable_shared_from_this<T> ? I can't seem to figure out why you wouldn't just create a std::shared_ptr<this> ?
Cppreference has a good example on why.
If you want to return a std::shared_ptr of this while *this is already owned by a std::shared_ptr and you don't return shared_from_this() but return a new std::shared_ptr<T>(this) instead then you will end up with 2 shared pointers that don't know they're both owning the same object and thus the use_count() will be wrong which will cause a double delete, which is undefined behavior.
Related
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Is there a way other than traits to add methods to a type I don't own?
(2 answers)
How can I wrap another type and add fields and methods to it?
(3 answers)
How to print a Vec?
(7 answers)
Closed 2 years ago.
I have some struct Animal. I want to implement some methods on Vec<Animal>. I believe the correct way to do this is to create a new wrapper object called Animals. What is the correct object to make this wrapper, though? A struct? An enum? Something else?
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What does an underscore and interface name after keyword var mean?
(2 answers)
Closed 4 years ago.
Little bit confused with this code.
var _ QueryAppender = (*selectQuery)(nil)
I found this code in pg-go
repository and don't know why QueryAppender declared that way. Please explain me what is the use cases when I should declare variables that way.
This doesn't do anything at runtime, but unless the *selectQuery type satisfies the interface QueryAppender, compilation will fail. It's a kind of static assertion.
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Difference between http.Handle and http.HandleFunc?
(4 answers)
Closed 5 years ago.
I'm trying to understand the differences between Handle and HandleFunc.
Other than the differences, when would you use one over the other when building a Go web app?
https://golang.org/pkg/net/http/#Handle
You'd use whichever one fits your handler implementation. If you've implemented your handler as a function, you'd use HandleFunc; if you've implemented it as a type with a ServeHTTP method, you'd use Handle.
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Blocks and yields in Ruby
(10 answers)
Closed 8 years ago.
Yield seems to be neither object nor method. What is it? How does it access the block that is passed as an argument to the method?
yield is a keyword, just like while or end or return.
"How" it accesses the block is not really interesting, no more than "how" a return keyword delivers a value to the calling context, or "how" an end keyword closes a block - unless you want to dive into development of Ruby interpreter itself. The important bit for a Ruby programmer is just that that's what it does.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Get list of a class' methods
Suppose I haven't any reference on hand, and I want to see all the methods in the built-in File class, is that simply available?
---------------------------EDIT---------------------------
answered in Get list of a class' instance methods
Sure, try:
File.methods
And if you have the awesome_print gem installed then it formats the list nicely and provides extra information.