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copied!<p>Value-type values for a class <em>have</em> to live together with the object instance in the managed heap. The thread's stack for a method only lives for the duration of a method; how can the value persist if it only exists within that stack?</p> <p>A class' object size in the managed heap is the sum of its value-type fields, reference-type pointers, and additional CLR overhead variables like the Sync block index. When one assigns a value to an object's value-type field, the CLR copies the value to the space allocated within the object for that particluar field.</p> <p>Take for example, a simple class with a single field.</p> <pre><code>public class EmbeddedValues { public int NumberField; } </code></pre> <p>And with it, a simple testing class.</p> <pre><code>public class EmbeddedTest { public void TestEmbeddedValues() { EmbeddedValues valueContainer = new EmbeddedValues(); valueContainer.NumberField = 20; int publicField = valueContainer.NumberField; } } </code></pre> <p>If you use the MSIL Disassembler provided by the .NET Framework SDK to peek at the IL code for EmbeddedTest.TestEmbeddedValues()</p> <pre><code>.method public hidebysig instance void TestEmbeddedValues() cil managed { // Code size 23 (0x17) .maxstack 2 .locals init ([0] class soapextensions.EmbeddedValues valueContainer, [1] int32 publicField) IL_0000: nop IL_0001: newobj instance void soapextensions.EmbeddedValues::.ctor() IL_0006: stloc.0 IL_0007: ldloc.0 IL_0008: ldc.i4.s 20 IL_000a: stfld int32 soapextensions.EmbeddedValues::NumberField IL_000f: ldloc.0 IL_0010: ldfld int32 soapextensions.EmbeddedValues::NumberField IL_0015: stloc.1 IL_0016: ret } // end of method EmbeddedTest::TestEmbeddedValues </code></pre> <p>Notice the CLR is being told to <strong>stfld</strong> the loaded value of "20" in the stack to the loaded EmbeddValues' NumberField field location, directly into the managed heap. Similarly, when retrieving the value, it uses <strong>ldfld</strong> instruction to directly copy the value out of that managed heap location into the thread stack. No box/unboxing happens with these types of operations.</p>

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