When looking at certain JavaScript code snippets, one may come across the following:
function allocate(bits) {
if ((bits & (bits - 1)) != 0) {
throw "Parameter is not a power of 2";
}
...
}
In essence, there exists a restriction on the value of input parameter bits, requiring it to be a power of two. Alternatively, instead of referring to it as a "constraint," it could be labeled as a validation that enforces the input to be a power of two.
On a side note, a similar concept of constraints can be applied in SQL as demonstrated below:
CREATE TABLE dbo.Payroll
(
ID int PRIMARY KEY,
PositionID INT,
Salary decimal(9,2),
SalaryType nvarchar(10),
CHECK (Salary > 10.00 and Salary < 150000.00)
);
ALTER TABLE dbo.Payroll WITH NOCHECK
ADD CONSTRAINT CK_Payroll_SalaryType_Based_On_Salary
CHECK ((SalaryType = 'Hourly' and Salary < 100.00) or
(SalaryType = 'Monthly' and Salary < 10000.00) or
(SalaryType = 'Annual'));
In both the SQL and JavaScript scenarios described above, the code execution happens at runtime to validate its correctness. While this behavior is confirmed for JavaScript, its occurrence in SQL might also be runtime-oriented.
The curiosity lies in exploring how a robust type system like TypeScript or another type-aware programming language can articulate the “power of two” constraint effectively. Ideally, transitioning it into a compile-time restriction presents an intriguing challenge. Is such a feat achievable? If yes, what methodologies are adopted by various languages to accomplish this? Any language example would suffice, serving primarily as a source of inspiration towards implementing this functionality within a custom language using its unique type system. Visualizing this as a compile-time constraint poses interesting questions around defining a specific “type,” denoting the “category of power of two integers.” Nonetheless, executing this task seamlessly remains a topic of exploration.