Product Perfect

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.

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

First 20 minutes

General Cap'n Proto IDL app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in Cap'n Proto IDL application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

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.

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 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.

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.

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.

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What you’re looking for early on

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

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

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

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

Next 20 minutes

Specific Cap'n Proto IDL development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

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.

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 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.

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.

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.

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At this point, a skilled Cap'n Proto IDL engineer should demonstrate strong problem-solving abilities, proficiency in Cap'n Proto IDL programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

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.

Wrap-up questions

Final candidate for Cap'n Proto IDL Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle Cap'n Proto IDL application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

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.

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.

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.

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.

Cap'n Proto IDL Consultive assessments

Cap'n Proto IDL Application Conversion Assessment Cap'n Proto IDL Application Integration Assessment Cap'n Proto IDL Data & Database Integration Assessment

Custom Cap'n Proto IDL development projects

Custom Cap'n Proto IDL App Conversion Cap'n Proto IDL Custom App Development Process App UI Design for Cap'n Proto IDL Facelifts

Hiring guide for Cap'n Proto IDL Engineers

Cap'n Proto IDL Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

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

Cap'n Proto IDL Consultive assessments

Custom Cap'n Proto IDL development projects