Technology
Discover facts about technology. Small discoveries that change the way you see familiar things.
Technology
Variable shadowing hides outer logic behind identical names
A function’s local variable can hide an outer variable with the same name, so references inside the function use the local one—a common source of bugs.
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C++ template compiling takes exponentially longer to run
Templates let C++ generate code during compilation, so heavily templated projects can take much longer to build—sometimes hours.
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Hardcoded magic numbers make codebase maintenance awful
When a number has no explanation, the next developer may be afraid to change it—even if it sits in the middle of a critical function.
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Modulo operations on negative values differ by language
Python, C, and JavaScript can give different remainders for negative numbers, so the same-looking operation may behave differently across languages.
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Why 0.1 plus 0.2 isn't 0.3
Binary floating-point numbers can't represent some decimal fractions exactly. So in many programming languages, 0.1 + 0.2 produces a number slightly different…
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Unicode updates constantly break legacy string parsing
When Unicode adds new characters or modifiers, text validators built around older character lists may reject them or handle them incorrectly.
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SQL range queries include both the start and end values
Unlike half-open ranges common in programming, SQL’s BETWEEN includes both endpoints, a difference that can trip up date queries.
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Global variables remain accessible from absolutely anywhere
Because any function can change a global variable, its value can shift far from where it was declared, making bugs harder to trace.
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Unix environments use /dev/null as a data black hole
Writing data to /dev/null makes it disappear; the special file discards anything sent to it. It's a handy destination when software needs to suppress output,…
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SQL databases treat NULL as unequal to another NULL
A NULL represents an unknown value, so SQL can't determine whether two NULLs are equal. To test for one, developers use `IS NULL`.
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Version control systems allow totally empty commits
Git can create an empty commit with a special flag, recording an event in the project history even when no files have changed.
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JavaScript sorts numbers alphabetically by default
Without a comparator function, JavaScript converts values to strings, so [10, 2, 1] sorts as 1, 10, 2 rather than numerically.
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C's rand function is surprisingly predictable
The function follows a mathematical sequence, so its output can repeat predictably rather than being truly random.
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Excel preserves a leap day that never happened
Earlier spreadsheet software treated 1900 as a leap year, and Excel preserves the error so dates in old files don’t shift.
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Large floating point numbers lose single digit precision
Floating-point numbers have limited precision, so a sufficiently large value can be spaced so far from its neighbors that adding 1 rounds back to the same…
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Pre-incrementing variables executes faster than post
When the old value isn't needed, `++i` avoids returning it; `i++` returns the pre-increment value, which can require a temporary for some types.
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Bogobogosort turns sorting into an exercise in wasted effort
The joke algorithm repeatedly sorts a smaller prefix, checks the next element, and reshuffles when the pieces fail to fit. Even checking progress can send it…
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Dynamic typing allows passing text strings into math
In a dynamically typed language, a text string may be passed to a subtraction function without being rejected upfront; the error may appear only when the code…
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Functional programming absolutely forbids mutating values
In pure functional programming, values are immutable: updating a counter means creating a new value rather than changing the old one.
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Maximum code test coverage still permits fatal logic flaws
A 100% coverage score means every line ran during testing, not that the program behaved as intended. A test can execute faulty logic without catching the…
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Why Java treats small integers differently
Java caches boxed integers from -128 through 127 so those values can be reused instead of newly allocated. This applies to boxed Integer objects, not all…
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Why a Singleton is basically a global variable
A Singleton limits a class to one instance, but using that instance as shared state can create the same coupling as a global variable.
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Boolean variables consume entire bytes instead of single bits
In many systems, a Boolean takes up a byte rather than a single bit because memory is addressed in byte-sized units. Some formats can pack Boolean values more…
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Boolean short-circuiting skips evaluating half the logic
In an OR expression, once the first condition is true, the program skips the second. That can save work, but it also means a function call placed there won’t…
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