st's blog

All expressions of 123456789 and signs +/- which value is 100

Submitted by st on

Suppose a string of ordered cyphers 123456789. You can insert signs "+" and "-" between any cyphers to make a correct arithmetical expression. The problem is to find all expressions which sum is 100.

This problem may be interesting for dynamic script languages having the function of a string expression evaluation.

E.g. solving in bash

When you still need use the singleton pattern?

Submitted by st on

The singleton pattern has come a long way since early 1990x. The programmer interview question "Write a singleton" in 1995 has evolved to "Write a lazy initialized singleton" in 2000x, and finished by "Why we do not use a singleton?" in 2010x.

Indeed, the unproved using of multiple singletons should be considered as antipattern. However, we still need singletons in some cases.

static_cast vs dynamic_cast: undefined behavior

Submitted by st on

Do not use static_cast when you cast from a basic class to a derived one. This may lead to undefined behavior. To handle the polymorphism, a virtual inheritance or a multiple inheritance case always use dynamic_cast instead.

The following short example shows the undefined behavior cases. This works with GCC, VC and online C++ shells:

Qt Test limitations and workarounds

Submitted by st on

Pros and cons

Why use Qt Test for unit testing and TDD (test-driven development)?

  • small testing framework (about 6K lines of source code);
  • seamless integration with QtCreator development environment;
  • full support of Qt framework including classes/types and signal/slots;
  • simple to start and use.

However, there are some drawbacks, too.

The brilliance and poverty of microservices

Submitted by st on

This is the revised translation of my article published in "ITWeek" magazine January 24, 2019.

An expert tries to know more and more about less and less until he knows absolutely everything about nothing. And a philosopher tries to know less and less about more and more until he knows nothing about everything.
Daniil Granin, "Going Inside a Storm"

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