[language-agnostic] What is Type-safe?

Type-safe means that the set of values that may be assigned to a program variable must fit well-defined and testable criteria. Type-safe variables lead to more robust programs because the algorithms that manipulate the variables can trust that the variable will only take one of a well-defined set of values. Keeping this trust ensures the integrity and quality of the data and the program.

For many variables, the set of values that may be assigned to a variable is defined at the time the program is written. For example, a variable called "colour" may be allowed to take on the values "red", "green", or "blue" and never any other values. For other variables those criteria may change at run-time. For example, a variable called "colour" may only be allowed to take on values in the "name" column of a "Colours" table in a relational database, where "red, "green", and "blue", are three values for "name" in the "Colours" table, but some other part of the computer program may be able to add to that list while the program is running, and the variable can take on the new values after they are added to the Colours table.

Many type-safe languages give the illusion of "type-safety" by insisting on strictly defining types for variables and only allowing a variable to be assigned values of the same "type". There are a couple of problems with this approach. For example, a program may have a variable "yearOfBirth" which is the year a person was born, and it is tempting to type-cast it as a short integer. However, it is not a short integer. This year, it is a number that is less than 2009 and greater than -10000. However, this set grows by 1 every year as the program runs. Making this a "short int" is not adequate. What is needed to make this variable type-safe is a run-time validation function that ensures that the number is always greater than -10000 and less than the next calendar year. There is no compiler that can enforce such criteria because these criteria are always unique characteristics of the problem domain.

Languages that use dynamic typing (or duck-typing, or manifest typing) such as Perl, Python, Ruby, SQLite, and Lua don't have the notion of typed variables. This forces the programmer to write a run-time validation routine for every variable to ensure that it is correct, or endure the consequences of unexplained run-time exceptions. In my experience, programmers in statically typed languages such as C, C++, Java, and C# are often lulled into thinking that statically defined types is all they need to do to get the benefits of type-safety. This is simply not true for many useful computer programs, and it is hard to predict if it is true for any particular computer program.

The long & the short.... Do you want type-safety? If so, then write run-time functions to ensure that when a variable is assigned a value, it conforms to well-defined criteria. The down-side is that it makes domain analysis really difficult for most computer programs because you have to explicitly define the criteria for each program variable.

Examples related to language-agnostic

IOException: The process cannot access the file 'file path' because it is being used by another process Peak signal detection in realtime timeseries data Match linebreaks - \n or \r\n? Simple way to understand Encapsulation and Abstraction How can I pair socks from a pile efficiently? How do I determine whether my calculation of pi is accurate? What is ADT? (Abstract Data Type) How to explain callbacks in plain english? How are they different from calling one function from another function? Ukkonen's suffix tree algorithm in plain English Private vs Protected - Visibility Good-Practice Concern

Examples related to programming-languages

What is the difference between syntax and semantics in programming languages? Scripting Language vs Programming Language Difference between "enqueue" and "dequeue" encapsulation vs abstraction real world example What's the name for hyphen-separated case? c++ array assignment of multiple values What is the first character in the sort order used by Windows Explorer? What is duck typing? What programming language does facebook use? Which programming languages can be used to develop in Android?

Examples related to computer-science

HTML5 Canvas background image What exactly does big ? notation represent? Fixed point vs Floating point number What are the differences between a program and an application? What do we mean by Byte array? How to determine the longest increasing subsequence using dynamic programming? What is "entropy and information gain"? What are the differences between NP, NP-Complete and NP-Hard? What is the difference between statically typed and dynamically typed languages? What is “2's Complement”?

Examples related to terminology

The differences between initialize, define, declare a variable What is the difference between a web API and a web service? What does "opt" mean (as in the "opt" directory)? Is it an abbreviation? What's the name for hyphen-separated case? What is Bit Masking? What is ADT? (Abstract Data Type) What exactly are iterator, iterable, and iteration? What is a web service endpoint? What is the difference between Cloud, Grid and Cluster? How to explain callbacks in plain english? How are they different from calling one function from another function?

Examples related to type-safety

What is the difference between a strongly typed language and a statically typed language? Type safety: Unchecked cast What is Type-safe? Generic type conversion FROM string