Articles

How C# and Java exceptions, Go’s error values and Rust’s Result carry one failure through a service, what each compiler checks, what failure costs, measured, and where to handle errors, log them and turn them into responses.

How to design types so impossible data can’t be built: sum types, exhaustive matching, newtypes, parsing at the boundary and typestate, in C#, Java, Go and Rust, with what each compiler actually says when a case is missed.

Why implementation inheritance breaks, shown in running Java code; how interfaces, Go’s embedding, Rust traits and plain functions abstract without it; and what static and dynamic dispatch cost, measured in Rust, Go and C#.

What each SOLID principle originally said, who said it, and how it gets misread. Liskov substitution broken in running code and in Java and .NET’s own libraries, dependency inversion measured with the Go build tool, and each principle in C#, Java, Go and Rust.

What makes a change cheap or expensive. Parnas’s information hiding, rebuilt in Go and measured; coupling and cohesion as first defined in 1974; deep and shallow modules; DRY as knowledge; and how C#, Java, Go and Rust enforce a module boundary.

A repeatable method for any system design, at work or in an interview. Clarify requirements, estimate, define the API and data, draw the high-level design, go deep on the risky part, and name the trade-offs, worked through a ticket on-sale on PostgreSQL.

An API is a contract you can’t easily take back. Learn HTTP method and status semantics, Problem Details errors, ETags against lost updates, idempotency keys tested on PostgreSQL, offset vs cursor pagination measured, and when REST, gRPC or GraphQL fits.

TCP gives order and reliability at a cost; UDP gives neither. Learn head-of-line blocking, slow start, HTTP/1.1 vs HTTP/2 vs HTTP/3 measured on a lossy network, connection pools and ports, and when to use polling, SSE or WebSockets.

Fast” and “reliable” can’t be designed for; p99 under 300 ms and 99.9% of requests succeeding can. Learn percentiles, tail latency, why busy servers get slow, availability nines, SLOs, and back-of-the-envelope estimates.

Opening a web page takes a DNS lookup, a TCP handshake, a TLS handshake, and a trip through load balancers, caches, app servers and databases. Follow one real request, measured step by step, and see where the time goes.