# Andrei Alexandrescu

Tudor Andrei Cristian Alexandrescu (born 1969) is a Romanian-American C++ and D language programmer and author. He is particularly known for his pioneering work on policy-based design implemented via template metaprogramming. These ideas are articulated in his book Modern C++ Design and were first implemented in his programming library, Loki. He also implemented the "move constructors" concept in his MOJO library. He contributed to the C/C++ Users Journal under the byline "Generic<Programming>".
He became an American citizen in August 2014.

## Education and career

Alexandrescu received a B.S. degree in Electrical Engineering from Polytechnic University of Bucharest (Universitatea Politehnica din București) in July 1994.
His first article was published in the C/C++ Users Journal in September 1998. He was a program manager for Netzip, Inc. from April 1999 until February 2000. When the company was acquired by RealNetworks, Inc., he served there as a development manager from February 2000 through September 2001.
Alexandrescu earned a M.S. (2003) and a PhD (2009) in computer science from the University of Washington.
In 2006 Alexandrescu began assisting Walter Bright on the development of the D programming language. He released a book titled The D Programming Language in May 2010.
From 2010 to 2014, Alexandrescu, Herb Sutter, and Scott Meyers ran a small annual technical conference called C++ and Beyond.
Alexandrescu worked as a research scientist at Facebook for over 5 years, before departing the company in August 2015 in order to focus on developing the D programming language.
In January 2022, Alexandrescu began working at Nvidia as a Principal Research Scientist.

## Contributions
### The D Programming Language

Along with Walter Bright, Andrei has been one of the two main designers of the D Programming Language, and the principal maintainer of the standard library Phobos from 2007 to 2019. He is the founder of the D Language Foundation. His contributions include the ranges module. He is the author of "The D Programmming Language" book.

### Expected

Expected is a template class for C++ which is on the C++ Standards track. Alexandrescu proposes Expected<T> as a class for use as a return value which contains either a T or the exception preventing its creation, which is an improvement over use of either return codes or exceptions exclusively. Expected can be thought of as a restriction of sum (union) types or algebraic datatypes in various languages, e.g., Hope, or the more recent Haskell and Gallina; or of the error handling mechanism of Google's Go, or the Result type in Rust.
He explains the benefits of Expected<T> as:
* Associates errors with computational goals
* Naturally allows multiple exceptions in flight
* Switch between "error handling" and "exception throwing" styles
* Teleportation possible across thread boundaries, across nothrow subsystem boundaries and across time (save now, throw later)
* Collect, group, combine exceptions

#### Example

For example, instead of any of the following common function prototypes:
int parseInt(const string&); // Returns 0 on error and sets errno.
or
int parseInt(const string&); // Throws invalid_input or overflow
he proposes the following:
Expected<int> parseInt(const string&); // Returns an expected int: either an int or an exception

### Scope guard

From 2000 onwards, Alexandrescu has advocated and popularized the scope guard idiom. He has introduced it as a language construct in D. It has been implemented by others in many other languages.