Month: October 2022

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Solid

  • The single-responsibility principle – piece of software should have only one responsibility
  • The open–closed principle – things should be open for extension but closed for modification
  • The Liskov substitution principle – changing interface implementation should not brake software
  • The interface segregation principle – it is better to have more specialized interfaces than single big one
  • The dependency inversion principle – dependencies should be abstracted via interfaces

Further read:

https://en.wikipedia.org/wiki/SOLID

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.NET/C# interview questions

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Equals and GetHashCode

Custom implementation is usually only necessary if default, reference equality is not enough. In example:

  • entities value based equality
  • value equality of deserialized objects
  • custom comparisons based on other criterias
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public class ImaginaryNumber : IEquatable<ImaginaryNumber>
{
public double RealNumber { get; set; }
public double ImaginaryUnit { get; set; }
public override bool Equals(object obj)
{
return Equals(obj as ImaginaryNumber);
}
public bool Equals(ImaginaryNumber other)
{
return other != null &&
RealNumber == other.RealNumber &&
ImaginaryUnit == other.ImaginaryUnit;
}
public override int GetHashCode()
{
return HashCode.Combine(RealNumber, ImaginaryUnit);
}
}
public class ImaginaryNumber : IEquatable<ImaginaryNumber> { public double RealNumber { get; set; } public double ImaginaryUnit { get; set; } public override bool Equals(object obj) { return Equals(obj as ImaginaryNumber); } public bool Equals(ImaginaryNumber other) { return other != null && RealNumber == other.RealNumber && ImaginaryUnit == other.ImaginaryUnit; } public override int GetHashCode() { return HashCode.Combine(RealNumber, ImaginaryUnit); } }
public class ImaginaryNumber : IEquatable<ImaginaryNumber>
{
    public double RealNumber { get; set; }
    public double ImaginaryUnit { get; set; }

    public override bool Equals(object obj)
    {
        return Equals(obj as ImaginaryNumber);
    }

    public bool Equals(ImaginaryNumber other)
    {
        return other != null &&
               RealNumber == other.RealNumber &&
               ImaginaryUnit == other.ImaginaryUnit;
    }

    public override int GetHashCode()
    {
        return HashCode.Combine(RealNumber, ImaginaryUnit);
    }
}