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@richlander
Last active Oct 11, 2021
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Battery example using 'with'
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net5.0</TargetFramework>
<LangVersion>preview</LangVersion>
<Nullable>enable</Nullable>
</PropertyGroup>
</Project>
using System;
Battery battery = new("CR2032", 0.235, 100);
Console.WriteLine (battery);
while (battery.RemainingCapacityPercentage > 0)
{
Battery updatedBattery = battery with {RemainingCapacityPercentage = battery.RemainingCapacityPercentage - 1};
battery = updatedBattery;
}
Console.WriteLine (battery);
public record Battery(string Model, double TotalCapacityAmpHours, int RemainingCapacityPercentage);
@richlander
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richlander commented Sep 15, 2020

Produces the following output:

PS D:\git\batteryrecord> dotnet run
Battery { Model = CR2032, TotalCapacityAmpHours = 0.235, RemainingCapacityPercentage = 100 }
Battery { Model = CR2032, TotalCapacityAmpHours = 0.235, RemainingCapacityPercentage = 0 }

@Aaron-Lathrop
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Aaron-Lathrop commented Nov 11, 2020

I'm confused, my understanding was that records are immutable and yet here we see battery being reassigned and effectively mutated.

Granted the original data in memory battery pointed to is in tact which will presumably be cleaned up by the GC.

Is this the point, to allow battery to have a reassigned reference for convenience as well as keeping memory cleaned up?

@empz
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empz commented Nov 12, 2020

I'm confused, my understanding was that records are immutable and yet here we see battery being reassigned and effectively mutated.

Granted the original data in memory battery pointed to is in tact which will presumably be cleaned up by the GC.

Is this the point, to allow battery to have a reassigned reference for convenience as well as keeping memory cleaned up?

Inmutable means you can't modify its properties. It doesn't mean you can't reassign a variable to a new record. The with is basically generating a clone of the battery but with a modified RemainingCapacityPercentage.

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