Tutorials covering programming languages, type systems, architecture, tooling, and the patterns used to build software that lasts. Each chapter is standalone, built around real examples and verified facts.
Variance describes how subtype relationships between types propagate through containers — arrays, functions, promises, and generics. If Dog is a subtype of Animal, is Dog[] a subtype of Animal[]? Is () => Dog a subtype of () => Animal? Is (x: Animal) => void a subtype of (x: Dog) => void? The answers depend on…
The provide() and the inject() pair makes the value available deep in the tree, but the key is a string by default, and the string is not the type-safe. The inject(‘theme’) returns the unknown, and the TypeScript cannot check the type. The developer must cast the value, and the cast is the runtime risk. The…
The previous chapter introduced Observables and the operator pipeline. This chapter goes deeper into the two largest categories of operators: transformation and filtering. Transformation operators change the values that flow through the stream — map converts each value, scan accumulates, switchMap and its siblings flatten inner Observables. Filtering operators decide which values continue — filter…
These two media features let you adapt styles based on the accuracy of the pointing device and the pixel density of the display — essential for touch-friendly interfaces and high-DPI screens. Overview of Features Feature Description Values pointer Accuracy of the primary pointing device none, coarse, fine resolution Pixel density of the output device dpi,…
A Future delivers exactly one value — or one error — at one point in time, and then it is done. A Stream delivers a sequence of values over time. The difference is not just quantity. A future is a placeholder for a single asynchronous result; a stream is a channel for asynchronous events. A…
Docker Compose begins with a single file. A compose.yaml file describes an entire application stack — every service, network, volume, and configuration — in declarative YAML. Instead of running docker run commands one by one, with all the flags, environment variables, port mappings, and network connections remembered separately, Compose reads the file and creates the…
The this keyword is one of the most confusing parts of JavaScript — until you understand one simple rule: this is determined by how a function is called, not where it’s defined. Once you internalize that rule, everything else falls into place. Key point: this refers to the execution context of a function — the…
The mysql2 package is the successor to the original mysql driver, rewritten for performance and modern JavaScript support. It is mostly API-compatible with the older library, so migration is usually a matter of changing the import, but it adds features that the original lacks: native Promise support, prepared statements with automatic caching, and a more…
useState works well when a component manages one or two independent values. A boolean for a modal, a string for an input, a number for a counter — each is a separate useState call, each updates independently, and the logic that changes each value is simple enough to live inline in an event handler. But…
Two trait mechanisms make Rust’s abstraction system more powerful than a simple set of method signatures. The first is default implementations: a trait method can have a body, so implementors are not required to write it. The second is supertraits: a trait can require that any type implementing it also implements another trait. Together, they…