#type conversion

There is a bunch of syntax that makes various JavaScript conversion statements shorter, but in my opinion, harder to understand. Though it is still useful to know about them when reading some library's code or rare cases like having to look through minified code.

Below is a list of these with the shorthand version followed, by the longer more understandable equivalent. First is Number:

const number = '1234'; console.log(+number); console.log(~~number); console.log(number^0); console.log(number|0); console.log(number>>0); console.log(number>>>0); console.log(number<<0); console.log(-number * -1); console.log(Number(number)); // 1234 (In both cases)

Then Boolean:

const setting1 = 'false';// Anything non-empty will be true console.log(!!setting1); console.log(Boolean(setting1)); // true (In both cases) const setting2 = '';// Or empty string console.log(!!setting2); console.log(Boolean(setting2)); // false (In both cases)

I think it is best to use exact checks instead of relying on any type boolean conversion in almost all cases. This way you don't have to memorize what is considered truthy or falsy. Next is String:

console.log(number + ''); console.log(String(number)); // '1234' (In both cases) const now = new Date(); console.log(now + ''); console.log(String(now)); // Your current time (In both cases)

In other words instead of a custom strategy in each case, just call the type constructor. There does not seem to currently be any shorthand conversions for the Null, Undefined or Symbol data types.

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One of the most criticized "feature" in C++ is that, a constructor which may accept one argument IS an implicit conversion function from the argument type T to the class type U. For example:

struct A { A(int, int = 4) {} }; void f(A) { } f(3); // f(A) is called

Such a "feature" is terribly bad. It looks like something designed to disable the compilers' type checking and to mess up the overloading set. But, all the criticisms are targeting the "implicit" aspect of this feature. I haven't seen an argument to criticize the "conversion" part.

My argument is, for short,

Implicit conversion makes sense.

Explicit conversion makes no sense.

Let's define a type as a set of all the possible values and a set of all the possible operations which deal with the values. Now, say if we have two types, int and list<long>, is that possible to convert an int n to a list<long>? Oh, maybe a list of n zeros. But wait, why zeros? And, what if I expect a {n}? See? If we allow one possible value set to be converted to an arbitrary possible value set, the semantics of the conversions are arbitrary and multiple, but the explicit conversion can only carry one semantics.

So that's why I say explicit conversion makes no sense. To express the meaning of an arbitrary conversion, the conversion function has to be named in some way to connect the two types involved, like list<long>::from_size(n), while an explicit conversion function is only named in a meaningless way (list<long>(n)).

But in one situation, a conversion is not arbitrary, and it can be safely and implicitly established from type T to U, if the possible value set of T is a subset of U's. Actually, C++ understands this theory, and that is why C++ allows an object of a derived class to be implicitly converted to an object of the base class, since an object of a derived class is supposed to be able to be used anywhere in place of an object of the base class.[1]

As you can see, the problem is not caused by "implicit"; the problem is caused by "conversion" -- mixing the conversion semantics into the constructors is a design error in C++.

So here are my suggestions:

Use implicit conversion for its well-defined semantics;

Prefer named functions/factories[2] over constructors.

Notes:

[1] Unfortunately, such a mechanism is broken if the derived class has a different representation, which results in a type punning, which simply breaks the type safety. However, pointer conversions and pointer to member conversions work.

Type Conversions

Type Conversions Function Grammar

<type>_to_<type>

Type Conversion Functions Examples

1> erlang:list_to_integer("54"). 54 2> erlang:integer_to_list(54). "54" 3> erlang:list_to_integer("54.32"). ** exception error: bad argument in function list_to_integer/1 called as list_to_integer("54.32") 4> erlang:list_to_float("54.32"). 54.32 5> erlang:atom_to_list(true). "true" 6> erlang:list_to_bitstring("hi there"). <<"hi there">> 7> erlang:bitstring_to_list(<<"hi there">>). "hi there"

List of all Type Conversion Functions