Cap'n Proto IDL Developer Hiring Guide

Hiring Guide for Cap'n Proto IDL Engineers

Ask the right questions to secure the right Cap'n Proto IDL talent among an increasingly shrinking pool of talent.

Cap'n Proto IDL (Interface Definition Language) is a high-performance data interchange format and capability-based RPC system. It is designed to be fast, efficient, and secure. The language allows developers to define data structures and interfaces in a language-neutral way, which can then be used across multiple programming languages. Cap'n Proto IDL's primary feature is its ability to perform "zero-copy" deserialization, making it extremely fast for reading data. It also supports advanced features like object-capability security model for defining access permissions and promises for asynchronous programming.

First 20 minutes

General Cap'n Proto IDL knowledge and experience

The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.

What is the purpose of the '@0' annotation in Cap'n Proto IDL?

The '@0' annotation is used to assign ordinal numbers to fields or methods. It helps in maintaining backward compatibility when the schema evolves.

Describe the difference between 'struct' and 'interface' in Cap'n Proto IDL.

'Struct' is a data structure that contains fields of various types, while 'interface' is a collection of methods that can be implemented by a struct.

How would you define a list in Cap'n Proto IDL?

In Cap'n Proto IDL, you define a list by specifying the type of the elements followed by a square bracket. For example, 'List(Text)' would define a list of text elements.

What are the basic data types supported by Cap'n Proto IDL?

Cap'n Proto IDL supports several basic data types including integers (int8, int16, int32, int64), floating point numbers (float32, float64), boolean, text, data, and enums.

How would you define a struct in Cap'n Proto IDL?

You define a struct in Cap'n Proto IDL by using the 'struct' keyword followed by the name of the struct and its fields enclosed in curly braces. Each field has a type, name and an ordinal number.

The hiring guide has been successfully sent to your email address.
Oops! Something went wrong while submitting the form.

What youre looking for early-on

Has the candidate demonstrated good communication skills during the interview?

Good communication skills are important in any role, as they will need to effectively communicate with their team and potentially clients.

Does the candidate have experience with the languages that Cap'n Proto supports, such as C++, Python, and JavaScript?

Having experience with these languages will allow the candidate to effectively work with Cap'n Proto IDL, as it supports these languages.

Has the candidate shown problem-solving skills during the interview?

Problem-solving skills are essential for any developer role. This will allow them to effectively troubleshoot and resolve any issues that may arise during their work.

Is the candidate able to explain how Cap'n Proto IDL compares to other data interchange formats?

This shows that the candidate has a broader understanding of data interchange formats and can make informed decisions about when to use Cap'n Proto IDL.

Can the candidate demonstrate experience with schema design in Cap'n Proto?

Experience with schema design is important as it is a key aspect of working with Cap'n Proto IDL. This will allow them to create efficient and effective data structures.

Does the candidate have a solid understanding of Cap'n Proto IDL?

This is crucial as the job role requires the candidate to work extensively with Cap'n Proto IDL. A strong understanding of this will ensure they can effectively perform their tasks.

Next 20 minutes

Specific Cap'n Proto IDL development questions

The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.

What are generics in Cap'n Proto IDL and how would you use them?

Generics in Cap'n Proto IDL are similar to templates in C++. They allow you to define methods that can operate on different types. You would use them by defining a method with a type parameter in an interface.

How would you define a method in an interface in Cap'n Proto IDL?

A method in an interface in Cap'n Proto IDL is defined by specifying its name, input parameters and return type. The parameters and return type are defined as anonymous structs.

How does Cap'n Proto IDL handle null values?

Cap'n Proto IDL doesn't have a null value for its types. Instead, optional fields can be used which are fields that may or may not hold a value.

What is the use of 'union' in Cap'n Proto IDL?

'Union' in Cap'n Proto IDL is used to define a type that can hold any one of several possible variants. It's a way to save space as only the space for the largest variant is reserved.

How would you define an enumeration in Cap'n Proto IDL?

An enumeration is defined in Cap'n Proto IDL using the 'enum' keyword followed by the name of the enumeration and its enumerators enclosed in curly braces.

The hiring guide has been successfully sent to your email address.
Oops! Something went wrong while submitting the form.

The ideal back-end app developer

What you’re looking to see on the Cap'n Proto IDL engineer at this point.

A skilled Cap'n Proto IDL engineer should demonstrate proficiency in data serialization, a strong understanding of interface definition questions (IDLs), and experience with distributed systems. Red flags include inability to articulate how Cap'n Proto improves over JSON or XML, or lack of familiarity with RPC protocols.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with Cap'n Proto IDL.

What does this simple Cap'n Proto IDL define?

@0xd3fbbf036af6040c;

struct Person {
  name @0 :Text;
  age @1 :UInt8;
}

This code defines a simple Cap'n Proto Interface Definition Language (IDL) structure named 'Person'. It has two fields: 'name' of type Text and 'age' of type UInt8.

What will be the output of this Cap'n Proto IDL code?

@0xb3fbbf036af6040c;

struct Employee {
  id @0 :UInt32;
  name @1 :Text;
  salary @2 :Float32;
}

const bob :Employee = {
  id = 123;
  name = "Bob";
  salary = 50000.0;
};

This code defines a structure 'Employee' with fields 'id', 'name', and 'salary'. It also defines a constant 'bob' of type 'Employee' and initializes it with specific values. The output will be an Employee object 'bob' with id as 123, name as 'Bob', and salary as 50000.0.

What does this Cap'n Proto IDL code do?

@0xb3fbbf036af6040c;

struct Department {
  name @0 :Text;
  employees @1 :List(Employee);
}

struct Employee {
  id @0 :UInt32;
  name @1 :Text;
  salary @2 :Float32;
}

This code defines two structures 'Department' and 'Employee'. 'Department' has a field 'employees' which is a list of 'Employee' objects. This represents a one-to-many relationship between Department and Employee.

What does this Cap'n Proto IDL code do?

@0xb3fbbf036af6040c;

interface Database {
  getEmployee @0 (id :UInt32) -> (result :Employee);
}

struct Employee {
  id @0 :UInt32;
  name @1 :Text;
  salary @2 :Float32;
}

This code defines an interface 'Database' with a method 'getEmployee' that takes an id of type UInt32 and returns an Employee object. It also defines a structure 'Employee' with fields 'id', 'name', and 'salary'. This represents a simple database interface for fetching Employee data.

What will be the output of this Cap'n Proto IDL code?

@0xb3fbbf036af6040c;

struct Employee {
  id @0 :UInt32;
  name @1 :Text;
  salary @2 :Float32;
}

const alice :Employee = {
  id = 456;
  name = "Alice";
  salary = 60000.0;
};

This code defines a structure 'Employee' with fields 'id', 'name', and 'salary'. It also defines a constant 'alice' of type 'Employee' and initializes it with specific values. The output will be an Employee object 'alice' with id as 456, name as 'Alice', and salary as 60000.0.

What does this advanced Cap'n Proto IDL code do?

@0xb3fbbf036af6040c;

struct Employee {
  id @0 :UInt32;
  name @1 :Text;
  salary @2 :Float32;
}

interface EmployeeDatabase {
  getEmployee @0 (id :UInt32) -> (result :Employee);
  addEmployee @1 (employee :Employee) -> (success :Bool);
  removeEmployee @2 (id :UInt32) -> (success :Bool);
}

This code defines a structure 'Employee' and an interface 'EmployeeDatabase'. The 'EmployeeDatabase' interface has methods for getting, adding, and removing an Employee. 'getEmployee' takes an id and returns an Employee object. 'addEmployee' takes an Employee object and returns a boolean indicating success. 'removeEmployee' takes an id and returns a boolean indicating success. This represents a more complex database interface for managing Employee data.

Wrap-up questions

Final candidate for Cap'n Proto IDL role questions

The final few interview questions for a Cap'n Proto IDL candidate should typically focus on a combination of technical skills, personal goals, growth potential, team dynamics, and company culture.

How would you ensure backward compatibility when evolving a schema in Cap'n Proto IDL?

To ensure backward compatibility in Cap'n Proto IDL, you should never change the ordinal number of a field or method, never delete a field or method, and when adding new fields, always make them optional.

What is the purpose of 'annotations' in Cap'n Proto IDL?

Annotations in Cap'n Proto IDL are used to attach metadata to various elements of the schema. They can be used to influence code generation or to add documentation.

How would you handle errors in Cap'n Proto IDL?

Cap'n Proto IDL doesn't have built-in support for exceptions. Errors are usually handled by defining an 'error' field in the return type of a method.

Describe the difference between 'import' and 'using' in Cap'n Proto IDL.

'Import' is used to include another Cap'n Proto file, while 'using' is used to create an alias for a type defined in another file.

What is the purpose of 'const' in Cap'n Proto IDL?

'Const' in Cap'n Proto IDL is used to define constant values. The value of a 'const' cannot be changed after it is defined.

The hiring guide has been successfully sent to your email address.
Oops! Something went wrong while submitting the form.

Cap'n Proto IDL application related

Product Perfect's Cap'n Proto IDL development capabilities

Beyond hiring for your Cap'n Proto IDL engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in Cap'n Proto IDL projects, and can engage in multiple capacities.