feat: same-type auto-mapping — T → T without CreateMap

[cloud-hai-vo]

Problem

In DSP, code like mapper.Map<DeliveryProvider, DeliveryProvider>(provider) throws No mapping configured because there's no explicit CreateMap<DeliveryProvider, DeliveryProvider>(). This is a common pattern for cloning/copying objects.

Fix

When no mapping is found and source type == dest type, auto-compile a property-copy delegate on first use and cache it. Uses the same ExpressionBuilder infrastructure as explicit maps — same performance after first call.

// No CreateMap needed — just works
var copy = mapper.Map<DeliveryProvider, DeliveryProvider>(provider);
copy.Id == provider.Id    // true
copy != provider          // true (new instance)

How it works

1. MapSlow / MapInternal exhaust all registered maps (frozen, open generic, base-type, interface)
2. Before throwing, check if sourceType == destType
3. If yes, create a synthetic TypeMap and compile via ExpressionBuilder
4. Cache in ConcurrentDictionary with GetOrAdd (thread-safe, one compilation per type)
5. Subsequent calls hit FastCache (zero-overhead)

What it skips

Primitives, strings, enums, value types, collections, dictionaries — these don't need property-copy semantics.

Precedence

Explicit CreateMap<T, T>() always takes precedence. Auto-mapping is only used when no registration exists.

Test plan

• 355 tests pass across net8.0, net9.0, net10.0
• 7 new tests: property copy, single-type-arg, null source, nested objects, list elements, fast cache, explicit precedence

🤖 Generated with Claude Code

[github-actions]

📊 Benchmark Results

Generated: 2026-03-27 04:04 UTC  ·  Download full artifacts

Column guide:
Mean = average execution time  ·  Error = half of 99.9 % confidence interval  ·  StdDev = standard deviation  ·  Min / Median / Max = statistical range  ·  Ratio = vs Manual baseline (lower = closer to hand-written speed)  ·  RatioSD = ratio std dev  ·  Rank = 1 is fastest  ·  Gen0/1/2 = GC collections per 1 000 ops  ·  Allocated = managed heap per operation  ·  Alloc Ratio = allocation ratio vs baseline

🔵 Flat Mapping — 10-property object

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	16.82 ns	0.705 ns	0.039 ns	16.77 ns	16.82 ns	16.85 ns	1.00	0.00	1	0.0048	80 B	1.00
EggMapper	27.27 ns	2.500 ns	0.137 ns	27.11 ns	27.35 ns	27.35 ns	1.62	0.01	2	0.0048	80 B	1.00
AutoMapper	86.90 ns	3.536 ns	0.194 ns	86.67 ns	87.00 ns	87.01 ns	5.17	0.01	3	0.0048	80 B	1.00
Mapster	29.41 ns	5.039 ns	0.276 ns	29.21 ns	29.30 ns	29.73 ns	1.75	0.01	2	0.0048	80 B	1.00
MapperlyMap	16.56 ns	1.392 ns	0.076 ns	16.49 ns	16.55 ns	16.64 ns	0.98	0.00	1	0.0048	80 B	1.00
AgileMapper	505.50 ns	25.659 ns	1.406 ns	503.93 ns	505.93 ns	506.64 ns	30.06	0.09	4	0.0200	344 B	4.30
EggMapperGenerator	16.70 ns	4.110 ns	0.225 ns	16.47 ns	16.70 ns	16.92 ns	0.99	0.01	1	0.0048	80 B	1.00
EggMapperClassMapper	16.28 ns	2.956 ns	0.162 ns	16.11 ns	16.29 ns	16.43 ns	0.97	0.01	1	0.0048	80 B	1.00

🟡 Flattening — 2 nested objects → 8 flat properties

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	20.03 ns	3.925 ns	0.215 ns	19.78 ns	20.12 ns	20.18 ns	1.00	0.01	1	0.0048	80 B	1.00
EggMap	30.95 ns	1.864 ns	0.102 ns	30.84 ns	30.99 ns	31.03 ns	1.55	0.02	3	0.0048	80 B	1.00
AutoMapper	96.25 ns	2.028 ns	0.111 ns	96.14 ns	96.24 ns	96.36 ns	4.81	0.05	5	0.0048	80 B	1.00
Mapster	38.15 ns	5.476 ns	0.300 ns	37.81 ns	38.27 ns	38.37 ns	1.91	0.02	4	0.0048	80 B	1.00
MapperlyMap	25.47 ns	6.762 ns	0.371 ns	25.05 ns	25.67 ns	25.70 ns	1.27	0.02	2	0.0062	104 B	1.30
AgileMapper	530.13 ns	98.290 ns	5.388 ns	526.10 ns	528.03 ns	536.25 ns	26.47	0.34	6	0.0200	344 B	4.30

🟣 Deep Mapping — 2 nested address objects

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	59.69 ns	16.298 ns	0.893 ns	59.17 ns	59.19 ns	60.73 ns	1.00	0.02	1	0.0162	272 B	1.00
EggMapper	69.99 ns	15.189 ns	0.833 ns	69.21 ns	69.90 ns	70.87 ns	1.17	0.02	1	0.0162	272 B	1.00
AutoMapper	127.34 ns	6.103 ns	0.335 ns	127.01 ns	127.35 ns	127.68 ns	2.13	0.03	2	0.0162	272 B	1.00
Mapster	73.83 ns	5.473 ns	0.300 ns	73.54 ns	73.82 ns	74.14 ns	1.24	0.02	1	0.0162	272 B	1.00
MapperlyMap	54.46 ns	24.970 ns	1.369 ns	52.89 ns	55.17 ns	55.34 ns	0.91	0.02	1	0.0162	272 B	1.00
AgileMapper	539.20 ns	19.529 ns	1.070 ns	538.15 ns	539.16 ns	540.29 ns	9.03	0.12	3	0.0248	424 B	1.56

🟢 Complex Mapping — nested object + collection

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	76.10 ns	13.740 ns	0.753 ns	75.23 ns	76.50 ns	76.57 ns	1.00	0.01	1	0.0191	320 B	1.00
EggMapper	100.83 ns	12.826 ns	0.703 ns	100.02 ns	101.23 ns	101.24 ns	1.33	0.01	2	0.0191	320 B	1.00
AutoMapper	169.34 ns	27.747 ns	1.521 ns	168.14 ns	168.84 ns	171.05 ns	2.23	0.03	3	0.0196	328 B	1.02
Mapster	93.13 ns	18.509 ns	1.015 ns	91.98 ns	93.55 ns	93.87 ns	1.22	0.02	2	0.0191	320 B	1.00
MapperlyMap	76.87 ns	9.278 ns	0.509 ns	76.41 ns	76.78 ns	77.42 ns	1.01	0.01	1	0.0191	320 B	1.00
AgileMapper	572.99 ns	25.598 ns	1.403 ns	572.12 ns	572.24 ns	574.61 ns	7.53	0.07	4	0.0315	528 B	1.65

🟠 Collection — 100-item List<T>

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	1.849 μs	0.6793 μs	0.0372 μs	1.814 μs	1.843 μs	1.888 μs	1.00	0.02	1	0.5283	0.0172	8.65 KB	1.00
EggMapper	1.895 μs	0.1282 μs	0.0070 μs	1.889 μs	1.894 μs	1.903 μs	1.03	0.02	1	0.5283	0.0172	8.65 KB	1.00
AutoMapper	2.521 μs	0.3284 μs	0.0180 μs	2.501 μs	2.528 μs	2.535 μs	1.36	0.03	2	0.6065	0.0191	9.95 KB	1.15
Mapster	1.910 μs	0.2894 μs	0.0159 μs	1.896 μs	1.907 μs	1.927 μs	1.03	0.02	1	0.5283	0.0172	8.65 KB	1.00
MapperlyMap	1.928 μs	0.6417 μs	0.0352 μs	1.888 μs	1.943 μs	1.953 μs	1.04	0.02	1	0.5264	0.0153	8.65 KB	1.00
AgileMapper	2.949 μs	0.4470 μs	0.0245 μs	2.923 μs	2.952 μs	2.971 μs	1.60	0.03	2	0.5417	0.0153	8.91 KB	1.03

🟠 Collection — 100-item List<T>

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	5.695 μs	1.3237 μs	0.0726 μs	5.625 μs	5.690 μs	5.770 μs	1.00	0.02	1	1.6708	0.0916	27.4 KB	1.00
EggMapper	6.265 μs	2.0141 μs	0.1104 μs	6.140 μs	6.311 μs	6.346 μs	1.10	0.02	1	1.6708	0.0916	27.4 KB	1.00
AutoMapper	7.124 μs	1.0014 μs	0.0549 μs	7.061 μs	7.156 μs	7.156 μs	1.25	0.02	1	1.7548	0.1068	28.7 KB	1.05
Mapster	6.358 μs	3.0200 μs	0.1655 μs	6.185 μs	6.372 μs	6.516 μs	1.12	0.03	1	1.6708	0.0916	27.4 KB	1.00
MapperlyMap	5.796 μs	0.8013 μs	0.0439 μs	5.749 μs	5.802 μs	5.836 μs	1.02	0.01	1	1.6785	0.0992	27.42 KB	1.00
AgileMapper	5.446 μs	0.7086 μs	0.0388 μs	5.401 μs	5.465 μs	5.471 μs	0.96	0.01	1	1.0223	0.0610	16.72 KB	0.61

🟠 Collection — 100-item List<T>

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	18.61 μs	9.647 μs	0.529 μs	18.07 μs	18.63 μs	19.12 μs	1.00	0.03	1	5.2490	1.3123	85.99 KB	1.00
EggMapper	18.28 μs	6.372 μs	0.349 μs	17.91 μs	18.34 μs	18.60 μs	0.98	0.03	1	5.2490	1.3123	85.99 KB	1.00
AutoMapper	22.89 μs	1.476 μs	0.081 μs	22.80 μs	22.90 μs	22.96 μs	1.23	0.03	1	5.7678	1.4343	94.34 KB	1.10
Mapster	18.52 μs	8.079 μs	0.443 μs	18.01 μs	18.78 μs	18.78 μs	1.00	0.03	1	5.2490	1.3123	85.99 KB	1.00
MapperlyMap	20.04 μs	1.552 μs	0.085 μs	19.98 μs	20.00 μs	20.14 μs	1.08	0.03	1	5.2490	1.2817	86.02 KB	1.00
AgileMapper	21.59 μs	3.649 μs	0.200 μs	21.36 μs	21.67 μs	21.73 μs	1.16	0.03	1	5.2795	1.3123	86.25 KB	1.00

⚪ Startup / Configuration time

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
EggMapperStartup	1,348.285 μs	1,697.4918 μs	93.0453 μs	1,257.711 μs	1,343.525 μs	1,443.619 μs	1.003	0.08	3	3.9063	1.9531	95.26 KB	1.00
AutoMapperStartup	399.302 μs	962.9685 μs	52.7836 μs	338.423 μs	427.213 μs	432.271 μs	0.297	0.04	2	5.8594	-	104.34 KB	1.10
MapsterStartup	2.655 μs	0.4913 μs	0.0269 μs	2.624 μs	2.666 μs	2.674 μs	0.002	0.00	1	0.7019	0.0267	11.51 KB	0.12

EggMapper.Benchmarks.ColdStartBenchmark-report-github

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
EggMapper	1.321 ms	0.9105 ms	0.0499 ms	1.282 ms	1.304 ms	1.377 ms	1.00	0.05	1	5.8594	3.9063	96.75 KB	1.00
AutoMapper	4.361 ms	11.2128 ms	0.6146 ms	3.741 ms	4.371 ms	4.970 ms	3.30	0.42	2	15.6250	7.8125	310.99 KB	3.21
Mapster	4.092 ms	12.9330 ms	0.7089 ms	3.410 ms	4.041 ms	4.825 ms	3.10	0.48	2	39.0625	15.6250	757.22 KB	7.83

---

📝 Notes

• Each benchmark class is decorated with [MemoryDiagnoser] and [RankColumn].
• The global config (see src/EggMapper.Benchmarks/Program.cs) adds Min, Median, and Max columns.
• Manual is the hand-written baseline (ratio = 1.00). A ratio < 1 means faster than manual.
• Benchmarks run on GitHub-hosted runners — absolute times may vary between runs; focus on Ratio for comparisons.
• To reproduce locally:

  cd src/EggMapper.Benchmarks
  dotnet run --configuration Release -- --filter '*'