#type system

Back2Basics: Introduction to Scala Type System

As programmers, we often come across a concept called type inference. To begin with let me clarify that type inference is not something unique to Scala, there are many other languages like Haskell, Rust and C# etc that have this language feature. Going by the bookish definition “Type inference refers to the automatic deduction of the data type of an expression in a programming language”. Speaking…

I often hear the argument "Language X is/isn't a strongly typed language because Y". Often times this argument arises because the language is dynamically typed, and therefore it must not be static. Except that most dynamic languages today are strongly typed, even if it may not seem immediately obvious.

I often hear Python being cited as a weakly typed language because its function arguments don't require typing, or because you can assign a different type of value to the same variable name. One thing those people don't mention, is this:

>>> "hello" + 3 Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: Can't convert 'int' object to str implicitly

You actually need to manually convert the integer to a string before concatenating or else you'll get a type error. Weakly typed languages don't give you type errors.

Ruby does the exact same thing:

irb(main):001:0> "hello" + 3 TypeError: no implicit conversion of Fixnum into String from (irb):1:in `+' from (irb):1 from /usr/bin/irb:12:in `<main>'

And so does Common Lisp:

[1]> (+ "hello" 3) *** - +: "hello" is not a number

JavaScript by comparison just doesn't give a damn:

> "hello" + 3 'hello3'

One could argue that JS is strongly typed, it just has type coercion that converts things into the appropriate types before attempting to do an operation on them, which I guess is a fair point; after all the above example simply converts the number to a string before concatenating it with "hello". I mean both C# and Java do the same thing, they both implicitly call .toString() on an object if its string is needed, and nobody calls those languages "weakly typed".

What about PHP?

> "2" + 2; => 4

I don't know about you, but I don't think that's supposed to happen. And yet it does, because PHP isn't strongly typed. I have a feeling it's because everything in PHP is represented as a string internally to ease the burden of doing web-development. That also comes with the gotcha that any representation of a number, string or otherwise, is a legal number to do maths with.

That said, not just dynamically typed languages are weakly typed, a few static languages are too.

If you know C well enough, you'll soon realise that pretty much everything is a number internally, which can lead to some pretty freaky stuff if you do it with care.

Note the following example (C doesn't have an interactive mode like the others):

#include <stdio.h> #include <stdlib.h> #include <string.h> int main(void) { char *str = "Hello, World!"; // set target string char *current = str; // set head of pointer to beginning while (*current != 0) { // while the string isn't 0 printf("%c\n", *current); // print the string pointer as a char current = current + 1; // add 1 to the string } return EXIT_SUCCESS; }

What's gong on here, is that I'm treating the string pointer current like an integer, adding 1 to it every time I've printed it. And since I know a string ends in a '\0' in C, '\0' having the ascii value 0, I can just check for it as such. And for those not familiar, C doesn't have strings, it instead uses char arrays and/or char pointers for that.

"But that's just pointer manipulation" I hear you cry. I know! That's my point, you can do this with structs and unions as well if you know your way around their internal memory representation. That's why I'd argue that C isn't strongly typed. C essentially allows you to add a struct to a string and get out the sum of their memory locations; and if you're going by the principle of least astonishment, then that's definitely not what you'd expect would happen.

In short:

Strong typing: Obeys type rules, types can't be mixed implicitly

Examples: Erlang, Python, Ruby, Common Lisp, Haskell, OCaml

Weak typing: Ignores type rules, types can be mixed implicitly

Examples: PHP, C, JavaScript

Static typing: Explicitly stating the types, variables can't change their type

Examples: C, C++, Haskell, C#, Java, Scala, OCaml

Dynamic typing: Types not stated, variables can change their types

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Fire type is strong against Earth type: (Fire melts rock, sand, metal, and devours stuff like grass/wood/living things)

Earth type is strong against Air type ( earth is heavier (more dominant) element, as well as “killing two birds with one stone”)

Air type is strong against Water type (Breathing underwater)

Water type is strong against Fire type (Water puts out fire)

Indoor medium contain good terms nipping regions is parlous important. In this way by dint of ergonomics the floor temperature be expedient range between 19 to 29 degrees C and the gentle wind temperature should run between 20 in passage to 24 degrees C for first-rate efficiency. <\p>

There are two types apropos of indoor climate control sc convection complexion and sunny type. Convection significant form heats the air then straw is moved around the interiors. Convection type uses systems like radiators, blowers and fireplaces. Radiant hotness systems heat the floor using caelus, liquid or antelope.<\p>

A pivot system is a ultramodern and superior strategy to a convection type system. The extradition system heats the air and does not heat the flatten grounds the ideal system should heat the precipitate on top of than the air. In a perfusion system the soprano part tends to escape as it becomes lighter and moves towards the ceiling. Farther convection systems can be harmful to mortals pained from allergies or convulsion as tell is circulated. A convection temperament is not aesthetically good to cue at, escape hatch the radiant systems go underneath the story and are invisible. <\p>

Air Type Floor Heating System<\p>

In this planning the air is heated to a central radiator and lapsed through pipes underneath the ground floor. However investigate heating systems are not popular because he are unable to retain toast passing by time. Hence they are used moderately where little heat is imperative such as mildly withdrawn regions. <\p>

Cold sweat martlet Liquid Type Floor Heating System<\p>

In this type warm water is circulated inside pipes laid high the floor. Usually 5\8-inch tubes are used. The give out is loyal in a boiler and circulated by means of thermo siphon. Thermo bleed is a natural system in contemplation of flow water intrusive tubes. A small pump is familiar with to purge out with bubbles trapped in the tubes. There are cutoff valves in case you want to heat a particular room and not other rooms. The tubes usually have a life of 100 years and obligate very little maintenance. The same system quod be used to circulate chilled water if the weather becomes hot. This system is the most civic and electricity pool in regard to 40 in transit to 15% are plastic. Duplex telegraphy Type Overmaster Heating<\p>